Sensation

SENSATION. - From sensus, sensatio, Gk. αἴσθησις, it is the original and fundamental manifestation of psychic life, whereby there occurs the first form of the presence of things - of the world and of one's own body - to the consciousness of the living being. Beyond the biological significance that sensation has as a means of conservation, development and defence of life, it assumes in man a higher value, as the initial process of knowledge that supplies the matter and the real contents of thought (cf. Sum. Theol., 2ᵃ-2ᵃᶜ, q. 67, a. 2, c.).

I. SENSATION AS A PHYSIO-PSYCHIC PROCESS

The condition of consciousness in the world is its being and manifesting itself in dependence on the body; the original moment in which this fundamental "situation" of consciousness is revealed is sensation, which presents itself as a fact of consciousness, but with an intrinsic relation of causal derivation from a corporeal fact (of the organism, and, through it, of the physical universe). Sensation therefore presents to investigation a twofold direction of deepening: a) the determination of its conditioning and of its physio-psychic modalities (psychophysics and experimental psychology); b) the analysis of the state of consciousness as such and of the meaning it assumes in relation to the tasks and ends of personal existence (gnoseology, pedagogy, ethics, etc.). As a "conscious reaction to an organic modification", sensation is a physio-psychic process, and indeed the moment in which, with continuity of functions, the passage between the physical and the psychic is accomplished. The elements or conditions of this process are the organ, the stimulus, and the energy or psychic virtuality of the conscious subject.

The organ is, in a certain sense, the immediate corporeal subject of the faculty of sensing (αἰσθητήριον δὲ πρῶτον ἐν ᾧ ἡ τοιαύτη [αἰσθητική] δυνάμεις; Aristotle, De an., II, 12, 424 a 24). It is among the most differentiated structures of the living organism. It consists essentially of: a) a receptive apparatus (the peripheral nerve endings); b) the afferent nerve; c) the sensory centre (a notion that today is held to have not only anatomical but also physiological meaning). Peripheral endings, nerve and centre constitute an anatomical-functional unity whose task is to receive the impression of the stimulus, reacts to it by elaborating it, and in this way conditions the conscious response. For the different senses there exists a constancy of nerve-central reaction expressed by the law of J. Müller (1801-58): to stimuli of different nature a given organ always reacts according to its specific sensation.

The stimulus is an action (and consequent modification) produced upon the organ. Such action may derive: a) from external reality, and precisely from the modifications of bodies that act either by contact of their own mass (tactile sensations of resistance, pressure, etc.), or by chemical dissociation (sensations of taste and perhaps also of smell), or by transmission of vibratory movement (visual and acoustic sensations), b) The action-stimulus may also derive from phenomena that take place within the organ (e.g., processes of dissolution or degeneration of tissues; currents of action-reaction between cells in the centres, from which arise the representative states reproducing elements or complexes of external sensations). Not every activity of the physical world is capable of positing itself as a sense stimulus: electricity, radioactivity, magnetism do not act as specific stimuli on human sensibility. But moreover, even the specific stimulus (tactile, visual, auditory, etc.) is not capable of exciting the organ unless it reaches and exceeds minimum and maximum limits of intensity (minimum and maximum "threshold" of the stimulus). The nature of the physiological process that intervenes within the nerve endings, the afferent nerve, and still more in the microstructure of the cerebral centres, is obscure. It seems certain that the nervous current or wave of activity that runs through the sensory fibres is always accompanied by an electrical effect (cf. A. Edgar Douglas, The physical background of perception. Oxford-London 1952, Italian trans. Turin 1952, p. 24 ff.).

Psychic energy is the virtuality, proper to the living being, of reacting with a representation of consciousness to the peripheral-nerve-central modification. It is from this obscure virtuality - which is the first power of the being's presence to itself - that sensation proceeds as knowledge. In its conclusive and formal moment sensation is therefore the actualization and perfecting of the sentient being as such, activity and spontaneity, formal and representative becoming of the subject, which has its effective causality in the depth of life as the principle of immanence and of consciousness (cf. Aristot., De an., II, 5, 416 b 33; St. Thomas, In De an., II, lect. 11-12, ed. Pirotta, n. 367 ff.).

In sensation we must distinguish quality, quantity, and tone. Quality is the representative content proper to sensation: colour, sound, cold-hot, etc. (sensibles "proper"), movement, figure, form, magnitude (sensibles "common"); cf. Aristotle, De an., II, 6 and St. Thomas, in hunc loc.). Qualities belong to sensation not as activity, but as representation: "red", "cold" is not the sensing, the seeing (αἴσθησις) but the content or term of seeing and sensing (the "sensed", αἰσθητόν), whether or not such content has reality and consistency in itself independent of the representation. Quantity is the degree of intensity of a sensation; and it has its reason in the essential dependence of sensation itself on the stimulus, a physical and therefore quantitative fact. The relation between the quantity of the stimulus and the intensity of the sensation has been scientifically determined in the Fechner-Weber law: the quantitative variation of the stimulus necessary to determine a variation of intensity of the sensation is a constant ratio of the initial stimulus (in sensations of weight, e.g., ca. 1/3). This law is also expressed in the formula: to a geometric ratio of the stimulus there corresponds an arithmetic ratio of the sensation. The merely partial correspondence of the intensity of the sensation to the quantitative variations of the stimulus is related to the practical ends of the living being; but at the same time it confirms the "approximate" value of sensation, which involves a certain "reduction", for biological ends, of the totality of the characters of the stimulus.

"Tone" is the affective element (of pleasure or displeasure) inherent, in varying measure, in all sensations. Beyond the indicated fundamental properties, every sensation, as a process in time, has a duration, and spatial extension is essential to visual sensations.

II. CLASSIFICATION OF PROPER SENSIBLE SENSATION

The ancient classification, proceeding from an obvious consideration that takes account of the structural difference of the peripheral organs and the qualitative difference of the objects, distinguishes five kinds of sensation: tactile, gustatory, olfactory, auditory, visual: "sensus esse quinque audire soleo, videndi, audiendi, olfaciendi, gustandi atque tangendi... Partitio ista antiquissima est et fere in contionibus celebrata" (St. Augustine, De quant. animae, ch. 23, n. 41: PL 32, 1058; cf. Aristotle, De sensu et de sensato, ch. 3 and De an., II, 6, 418 a 7; Plato, Theaet., 156 b). However, Aristotle already observed that "touch contains in itself many different sensations" (Ἡ δ' ἄφη πλείους μὲν ἔχει διαφοράς: De an., II, 6, 418 13; cf. II, 11, 422 b 17 and Sum. Theol., 1ª, q. 78, a. 3 ad 3).

The modern classification, on the basis of the threefold criterion of the formal difference of qualities, the anatomical-functional diversity of the organ, and the specific difference of the physical stimulus, distinguishes the following principal forms of sensation: of contact-pressure, of temperature, of weight, of position, of movement, of pain; organic sensations; sensations of taste, of smell; auditory, visual sensations.

1. Sensations of pressure-resistance

The stimulus is a mechanical action of bodies on particular cutaneous and subcutaneous nerve endings, with the effect, it seems, of modifications of the osmotic state of the cells. The sensation is generally qualified according to the form and physical conditions of the object (sensation of hardness, roughness, smoothness, etc.). Through the experience it gives of an obstacle and of a resistance to one's own action, the sensation of pressure-resistance contributes to founding the conviction of the existence of the external world. 2) Sensations of temperature. Specific nerve endings correspond to them (Pacinian and Meissner corpuscles); the stimulus is the molecular vibrations of the surrounding (air) or touching body. Sensations of temperature have a subjective character: in a sensation of cold, heat, etc., the objectification of the stimulus is therefore nil; where it intervenes (e.g., in the sensation of cold through contact) it is due to concomitant tactile sensations. 3) Sensations of weight (baresthesia). They are mixed sensations of contact and pressure, but they also have a specific element; they are mostly associated with muscular and effort sensations. 4) Sensations of position (bathesthesia). They report the position of the parts of one's own body. They probably have an articular origin, but the general tone of innervation contributes to them, and principally visual-tactile representative associations. 5) Sensations of movement. Also called kinetic sensations, they report the passive and active movement (olventc) of one's own body and its limbs. They are principally of articular origin, but they also seem due to the modifications that intervene, following motor contraction, in the muscles, tendons and other dermic and endodermic tissues. They contribute to the clear perception of one's own body as a source of activity, and therefore to the fundamental sense of life. 6) Sensations of pain (acute, dull, burning, punctual, continuous, etc.). They are caused by more or less profound alterations in the tissues, on the part of mechanical, chemical, electrical agents... The nerve endings are specific, distinct from those responding to sensations of pressure and temperature. Sensations of pain have a more or less unpleasant affective tone (when they are of minimal intensity they can descend to a neutral affective level and even be slightly pleasant); they also have a teleological significance, as signals of dangers and offenses to the integrity of the organism and to existence itself. Together with sensations of contact, sensations of pain are therefore among the most necessary to life ("touch is the fundamental sense that is found in all animals... and of all it is the most necessary": Aristotle, De an., II, 2, 413 b 4 ff.; cf. St. Thomas, De verit., q. 22, a. 5). 7) Organic sensations. They manifest, with a rich variety of forms, the functions and conditions, normal and pathological, of the organism (sensations of hunger, thirst, well-being, tiredness, tension, relaxation, sexual sensations, etc.). The organ is the nerve endings diffused throughout the body; the stimulus is the physiological and microenergetic modifications in the organs, tissues and cells, determined by biological metabolism. Qualitatively simple, from the physiological point of view they are complex sensations, difficult to analyze: sensations of pressure, contact, temperature, muscular, etc. have a part in them; but their affective tone is specific, original. They condition the "behavior" of the animal and in man also, in part, the higher affective states. Together with sensations of pain they serve as a phenomenological basis for the concept of happiness, good, evil, etc. 8) With the name of cenesthesia (κοινή αἴσθησις, common sensation) modern psychology designates the immediate awareness (which can also be understood as the basic and undifferentiated form of organic sensations) that the animal has of its own body and of its general state: an indistinct, somewhat obscure sensation, which can be described as a vague and diffuse internal tactile sensation, with a slightly but positively pleasant tone. Through it the subject or the biological being has the first and concrete presence of itself, which the other specific sensations have the task of intensifying and differentiating; cenesthesia thus stands as the experiential foundation of the very concept of existence and of life. 9) Sensations of taste. The organ consists of particular nerve endings on the tongue (fungiform papillae) and palate; the stimulus, of bodily substances chemically dissolved. Already St. Thomas noted the affinity of taste with smell: « Odor enim et sapor quandam affinitatem habent » (In De sensu et de sensato, lect. 2, n. 23; cf. lect. 9, n. 118: « utrumque eorum est fere eadem passio »). The sensations of taste are subjective affections: they therefore present neither "external" objectification nor spatial determination. 10) Olfactory sensations. The organ consists of the nerve endings of the pituitary membrane; the stimulus, of particles of bodies in the gaseous state, introduced with respiration. In some animal species (bees, etc.) olfactory sensations have a predominance of meaning over all the others. In man they are secondary (« sensum olfactus peiorem habemus et per comparationem ad cetera animalia et per comparationem ad ceteros sensus qui in nobis sunt »: St. Thomas, ibid., lect. 9, n. 119). According to Pradines, taste and smell are "senses of need" insofar as « nous font connaître les choses comme répondant à nos besoins », that is, to the impulses that periodically drive us toward the search for and appropriation of the external conditions necessary for the preservation and perpetuation of our existence (Traité de psychol., I, 3rd ed., Paris 1948, p. 498). But it must be admitted that such finality is common, albeit with different manifestations, to all sensations (cf. St. Thomas, In De s. et de s., lect. 2, n. 24). 11) Auditory sensations. They derive from the excitations that the vibrations of bodies, transmitted through the air or another elastic medium, produce on the nerve endings (fibers of Corti) of the cochlear nerve. Homogeneous, regular vibrations give clear, distinct "sounds"; irregular, mixed vibrations give "noises", "din". Auditory sensations have a particularly synthetic character: elementary sounds (e.g., of the sea, wind) manage to merge into a single vast auditory sensation. In relation to time, individual sounds, through a certain "auditory memory", persist as sensations beyond their physical reality: a fact of extreme importance for language (v.), which would be impossible if the phonic elements (syllables and words) did not continue in the representative unity of the phrase and the period. Measure, rhythm and proportion have moreover conferred on auditory sensations a particular aesthetic value (music). 12) Visual sensations. They are determined by the luminous vibrations that excite, with a probably electric-vibratory effect, the nerve endings (cones and rods) of the retina. Individual wavelengths give elementary "colors"; the whole of the wavelengths of the spectrum gives "white, light"; to "black", which psychically has a positive value like every other chromatic sensation (the stimulus is either the very limit of a chromatic sensation or an internal excitation of the nerve), there corresponds physically only the absence of vibrations. Particularly in visual sensations the following must be noted: a) phenomena of fusion: vibratory stimuli corresponding to different colors, if they excite the retina simultaneously, determine a psychically simple response. b) Phenomena of contrast: visual sensations close in space or time influence and modify one another. c) Consecutive after-images: an intense visual sensation persists after the physical stimulus has ceased (the phenomenon is, to varying degrees, general for all sensations and must be referred to the persistence of the nervous excitation). d) Binocular vision with the effect of a single image was already referred by St. Thomas (In De s. et de s., lect. 19, n. 284) to the central unity of the organ. e) All visual sensations are spatial. Because of their immense synthetic capacity (the visual angle can embrace an infinity of objects), visual sensations play the principal part, in those who see, in the manifestation of the external world.

With the clear representation of distance (v. below) they stand in a certain way as a spatial amplification of the tactile perceptual sphere. They therefore constitute, from the objective point of view, the highest perfection of sensibility, and visual terms and images have been adopted to indicate the very activity and the values of thought (vision, idea, evidence, intuition, etc.).

The individual external sensations, because of their objective-functional discrimination, would not allow the subject that organic and unitary representation of objects which is necessary for a valid biological behavior in the physical environment of existence. External sensations therefore continue into the internal sensibility, which has the function of unification, representation, recollection with reference to time, and evaluation of the contents of external sensations (common sense, imagination, memory, reminiscence, estimative power, cogitative power; v. these entries, and cf. the lucid exposition in Sum. Theol., 1ª, q. 78, a. 4).

III. SPACE, MOVEMENT, TIME

Space (figure, size, shape) and movement (rest), which Aristotelian-Thomistic psychology qualifies as "common sensibles," since they are the object of several senses, constitute a further level of objective determinations of sensibility.

1. Space

Empirical theories (Berkeley, Spencer, Taine, Lotze, Wundt) regard space as a "secondary" datum, that is, derived from a constructive process of perception; nativistic theories (Aristotle, St. Thomas, a large part of modern psychology) affirm, within certain limits, the "original" (native) character of spatial representation. Nativism must not be confused with "apriorism" (Kant), which understands space as a subjective form conditioning experience a priori. It seems difficult to deny the original character of spatial representation. Even the empiricist explanation that derives space from the constructive movement of the organ does not in reality oppose nativism, inasmuch as the movement of the eye along the points bounding the object presupposes an extension that it determines, as figure or shape, but does not create as pure extension (moreover, the copious researches of Gestalt-and Ganzheitpsychologie have shown that formal structures themselves are in many cases given as global and unitary stimuli, so that even the visual apprehension of "form" often has an original character). The physiological antecedent of visual spatial sensation is the extended, spatially configured excitation of the stimulus on the retina. That the discontinuous extended, such as material reality perhaps is, comes to be represented by consciousness as continuous, is in accord with the law of "threshold" (already known to and discussed by Aristotle and St. Thomas: cf. De s. et de s., ch. 6), by which stimuli whose spatial distance is below the minimum distance discernible by the physio-psychic structure of the sense act as a single stimulus and therefore cause a continuous visual representation (the continuous, accordingly, as it is given in macroscopic experience, can be referred to the synthetic function of sensibility). The constructive activity of visual sensation is displayed to a greater degree in the perception of the third dimension. Distance and depth do not seem to be the object of elementary sensations (a luminous point in the darkness, without terms of reference, cannot be evaluated as to its distance), but are rather due to a perceptual elaboration (contributing to it are: binocular parallax; the different variation of the visual angle for near and far objects, when the eye moves in their direction; the reference of the apparent size of an object to its real, known size; the movement necessary to move toward the object, etc.). Tactile spatial perception seems to be essentially genetic-motor in nature. Pure contact sensation, not integrated by visual-tactile representations (imagination and memory generally intervene in the spatial construction of objects), does not give, at least in distinct form, the third dimension and the shape of objects: both are "constructed" through the representation to which the tactile organ (hand) gives rise as it traverses the surface bounding the object: such is, as is well known, spatial representation in the blind.

2. Movement

Movement, as a change of position of external objects in space, is a modality of the visual-tactile stimulus and therefore an original datum of sensation. But since, as pure variation of position, motion is relative and reversible, visual sensation alone does not of itself refer the real movement of an object. Even in sensations of movement a process of physio-psychic construction can intervene: a motionless stimulus acting on the retina from two nearby positions succeeding one another at a time interval below the differential threshold is seen not as two images but as a single one, in movement from the first to the second position (cinematograph and stroboscopic apparent movement); the movement in this case is a pure perceptual datum. The tactile sensation of movement is principally active, that is, dependent on the real movement of the organ (hand) over the object. More obscure - where the habitual integration of internal representational sensibility does not intervene - is the tactile sensation of passive movement (of the object over the organ).

3. Time

Phenomenologically, time is the duration of a phenomenon (object, sensation, datum, representation). The "before" and the "after," "beginning," "lasting," "ending" are essential modalities of experience, and therefore, concretely, time is given with experience itself: "tempus non sentitur quasi aliqua res permanens proposita sensui, sicut videtur color, magnitudo, sed propter hoc sentitur quod sentitur aliquid quod est in tempore" (St. Thomas, In De s. et de s., lect. 18, n. 271). In the concrete content of perception, through an abstractive intuition of spiritual consciousness, the real character of "duration" and of "succession" is grasped, and these thus come to be posited as universal representations. In its formality, time is therefore not the object of sensation, but it is nonetheless, as real duration, an objective character of all sensations. The Kantian doctrine of time and space as a priori forms of sensibility is therefore inexact. Time and space, as contents or concrete values, belong to the objects of real experience (time, moreover, to experience itself as successive psychic becoming in consciousness). The a priori of sensibility in relation to space and time is a function not thetic, but only constructive and organizational; and transcendence for sense must be understood as the perceptual-elaborative relation of the physio-psychic structures to the real stimulus.

IV. SENSATION IN THE HISTORY OF PHILOSOPHY

The problem of sensation, of its value and meaning, is fundamental in almost all currents of philosophical thought. The presocratics inclined toward sensism (v.), that is, toward the final reduction of all knowledge to sensation; they understood sensation, for the most part, in a passive and materialistic sense. For Empedocles the sensible qualities are physical emanations of things: "color is an efflux of figures, proportional to the eye and perceptible" (Men., 76, d; cf. Aristotle, De sensu et sensato, 2, 438 a 4, and De anima, I, 2). Similarly in Democritus (v.) to sense is to receive passively corporeal images (the εἴδωλα that enter the organ: cf. Diogenes Laertius, IX, 44). But already in Protagoras sensation is understood in an active sense: color, hot, hard, etc. "are nothing in themselves (καθ'αὐτὸ μηδέν) but arise from a mutual correspondence (of object and sense) and universally from movement" (Theaet., 157 a ff.; cf. 154 a, 156 b ff.). In Plato sensation is an affection of the body that makes itself present to the soul and therefore a principle in the soul of recollection (v.): "The being hidden (of the affections of the body) from the soul call it insensibility...; but when body and soul together fall into one and the same affection (ἐν ἑνὶ πάθει) and are moved together, this you would not wrongly call sensation" (Phil., 33 e and 34 a; cf. 30 a). In Aristotle the problem of sensation is developed with a wealth of analysis and observations. He overcomes the materialistic naturalism of the presocratics with the concept of sensation as "reception of sensible forms or images without the matter" (De an., II, 12, 424 a 18), a formula that corresponds, it seems, to the expression of medieval terminology: "recipere intentionaliter, obiective." Sensation for Aristotle is, to some extent, knowledge: ἡ δ'αἴσθησις γνῶσίς τις (De generat. animal., I, 23, 731 a 43); if it must be called alteration, "since it is manifest that sensation occurs by means of the body" (De sensu et sensato, 1, 436 b 6), it is nevertheless a "special alteration" ἀλλοίωσίς τις; ἡ ἑτέρου γένους ἀλλοίωσις (De an., II, 5, 416 b 34; 417 b 7); and if it involves a passive moment (πάσχειν, κινεῖσθαι: ibid., 416 b 34), it is nevertheless formally an immanent and perfective act of the sentient being (εἰς αὐτὸ ἐπίδοσις καὶ εἰς ἐντελέχειαν: ibid., 417 b 6). As for its biological significance, sensation is ordered to the preservation and defense of the animal (σωτηρίας ἕνεκεν: De sensu et sensato, 1, 436 b 20), but in man sensible knowledge is the objective condition of thought: "the intellect does not know external things except by means of sensation" (ibid., 6, 445 b 16-17; cf. De an., III, 8, 432 a 8: the fundamental anti-Platonic motif of Aristotelian epistemology). Stoicism, and even more so Epicureanism, resolve every spiritual activity into sensation, and therefore posit sensation itself as the norm and criterion of truth (cf. Diogenes Laertius, VII, 4 ff., and X, 31: "Epicurus posits as criteria of truth sensations, anticipations, affections"). Plotinus reaffirms sensation as an internal activity of the soul: "we understand sensations not as something we undergo (πάθη) but as activity concerning sensible impressions and as judgment" (Enn., III, 6, 1, 26). St. Augustine, in dependence on Plato, defines sensation as "passio corporis per seipsam non latens animam" (De quant. animat., ch. 25, n. 48: PL 32, 1063; cf. ch. 23, n. 41; ch. 30, n. 58), that is, an affection of the body that makes itself immediately present to consciousness: "Intendit se anima in tactum et eo calida, frigida, aspera, lenia, dura, mollia, levia, gravi sentit atque discernit" (ibid., ch. 33, n. 71: PL 32, 1074. Cf. De genes. ad litt., XII, 24: PL 34, 475, where Augustine seems to refer sensation to the soul alone: "Neque enim corpus sentit, sed anima per corpus, quo velut nuntio utitur ad formandum in seipsa quod extrinsecus nuntiatur"; cf. Sum. Theol., 1ᵃ, q. 84, a. 6). The statement "aliud est sentire, aliud cognoscere" (De quant. an., ch. 24, n. 45: PL 32, 1060) does not mean, in context, that sensation is not knowledge, but that a knowledge is possible which is not sensation: sensation is in itself true, to the extent that it is capable of apprehending reality, but that science does not belong to it "quam volunt intelligentia contineri remotamque a sensibus in mente vivere" (Contra acad., III, ch. 11, n. 26; cf. De vera relig., ch. 33 and 36). St. Thomas's doctrine on sensation is a deepening of Aristotelianism. Sensation is the first grade of knowledge, intrinsically conditioned by the corporeal organ: "anima nihil sentit sine corpore, quia actio sentiendi non potest procedere ab anima nisi per organum corporale." As the act of a corporeal organ, sense is a passive power: "quae nata est immutari ab exteriori sensibili" (ibid., q. 78, a. 3 c.): an immutation not only material-physical, but also spiritual-intentional: "ad operationem autem sensus requiritur immutatio spiritualis per quam intentio formae sensibilis fiat in organo sensus" (ibid.; cf. In De an., II, lect. 2ᵃ, ed. Pirotta, n. 553). Such "intentional" immutation (the "species impressa" of traditional terminology) is the stimulus itself insofar as it is an objective determination and formal principle of representation (cf. In De an., loc. cit., where St. Thomas develops the Aristotelian concept of sensation as "receptio formae sine materia"). Sensation is not, however, a purely passive moment: "sentire, quantum ad ipsam receptionem speciei sensibilis nominat passionem; sed quantum ad actum consequentem ipsum sensum perfectum per speciem, nominat operationem" (In I Sent., dist. 40, q. 1, a. 1). The term of sensitive representation can only be a corporeal "form" individuated in time and space: "obiectum cuiuslibet sensitivae potentiae est forma prout in materia corporali existens" (Sum. Theol., 1ᵃ, q. 85, a. 1, c.; cf. ibid., q. 75, a. 6, c.); "sensus autem non cognoscit esse nisi sub hic et nunc" (ibid., 1ᵃ-2ᵃ, q. 15, a. 1). In sensation, therefore, neither the universal nor truth in the formal sense is to be sought (ibid., 1ᵃ, q. 17, a. 2, c.; cf. De verit., q. 1, a. 11, c.). Nevertheless the value of sensation for human knowledge is fundamental, since through it the presence of the real to consciousness is brought about, and in sensible representations - which attain their highest richness and objective consistency in internal sensibility, particularly in the cogitative power — the intellect finds the concrete content for the intuition and abstraction of universal values (cf. especially, on this fundamental point of Thomist gnoseology, Sum. Theol., I, q. 84, a. 6-7, q. 85, a. 1; v. "GONOSCENZA: INDUZIONE"). In the Renaissance, sensation receives particular attention in the thought of Campanella (v.). Sensing (which is not a simple "passion" but a judging act: Metaph., I, Paris 1638, p. 42) is concrete and immediate knowledge, and therefore the foundation of true philosophizing: "sentire est praesentis obiecti notitia" (Theol., X, ch. 3, a. 5); "duce sensu philosophandum esse existimamus. Eius enim cognitio omnium certissima est, quia fit obiecto praesente" (Prodromus, Frankfurt 1617, p. 27). In modern philosophy, Descartes, having reduced the essence of the subject to a pure "thinking thing" (Med., VI), understands sensation as a "passive faculty of... receiving and recognizing sensible ideas" (ibid.). Organic sensations "ne sont autre chose que de certaines façons confuses de penser," dependent on the union and "mixture" of the spirit with the body, and to the sensations of the external world there correspond in bodies certain determinate properties, even if dissimilar from the sensations themselves (ibid.; cf. Passiones an., I, 23, and Princ. philos., IV, 189). For Spinoza, "the ideas that we have of external bodies indicate rather the constitution of our own body than the nature of external bodies" (Eth., II, prop. 16, coroll. 2). According to Malebranche, sensation is "une modification de notre âme par rapport à ce qui se passe dans le corps auquel elle est unie." Sensations therefore "ne sont que dans l'âme" (De la recherche de la vérité, I, ch. 13, §§ 1-2). In empiricism (v.) sensation is the primary source of knowledge and its contents acquire the principal value of reality. For Locke, "the first capacity of human intellect consists in this, that the mind is fitted to receive the impressions made on it, either by external objects through the senses, or by its own operations... On this foundation all notions are established" (Essay, II, ch. 1, § 24). Berkeley, having denied the existence of matter as a thing in itself, understands sensations as representations or "ideas" produced in our spirit by God himself. Material things are resolved into sensations: "light and colours, heat and cold, extension and figures, in a word the things we see and feel, are nothing but so many sensations, notions, ideas or impressions of sense" (Principles, § 5). For Hume, sensations are the original perceptions of the spirit, that is, impressions (Treatise, I, part 1, sec. 1, § 1). Sensations, together with "ideas," which are as it were their residue in the mind, are ultimately the only thing of which we have absolute certainty ("nothing is really present to the mind but its own perceptions": ibid., part 4, sec. 2, § 5). The senses "do not present their impressions as images of something distinct or independent or external" (ibid., § 3), and "it will always be impossible to decide with certainty whether [the impressions] arise immediately from the object, or are produced by the creative power of the mind, or are derived from the Author of our being" (ibid., part 3, sec. 5, § 1). In Kantian criticism, sensibility is "the capacity of receiving representations through the manner in which we are affected by objects," and sensation is "the effect of an object on the representative capacity, insofar as we are affected by it" (Kritik d. v. Vernunft, I, part 1, § 1). The representation of what is given in sensation is called by Kant "empirical" intuition: it presupposes a formal element (space, which is a priori in the mind): for outer sense, space; for inner sense (and for all sensations insofar as they are subjective experience), time: space and time are therefore "pure" intuitions, transcendental conditions for the possibility of the representation of objects in sensation (ibid., § 2 ff.). With the Kantian doctrine, the creative activity of the subject is affirmed in relation to reality as the object of our experience (phenomenon).

In Hegelian idealism, sensation indicates the first determination of the spirit, still immediate and without development according to the antithesis of an objective against the subject. It is "the form of the dull agitation of the spirit in its individuality devoid of consciousness and intellect" (Encycl., § 400). Everything that takes place in spiritual consciousness and in reason — Hegel affirms — has in a certain way "its source and origin in sensation," but only in the sense that sensation is the first and most immediate manner in which the contents of the spirit appear. Through sensation the I of consciousness (which is what belongs to being-for-self) is determined as spiritual corporeity; whereby sensing "is the healthy coexistence of the individual spirit in its corporeity" (ibid., § 401). Absolute interiority, therefore, and immanence of all the determinations that are given through sensation: "Sensations are... changes in the substantiality of the soul, posited in its being-for-self, which is identical with substantiality" (ibid., § 402). Rosmini (v.) distinguishes two modes of sensitive perception: a) there is the "fundamental" and universal "feeling" "by which we feel life to be in us" (Nuovo saggio, sec. 2, part 3, ch. 1, a. 1); it is a permanent and one activity, "always vigilant and actuated to feel the state, whatever it may be, of our sensitive body" (ibid., a. 3), and it results immediately "from the first individual conjunction of the spirit with an animal body" (ibid.). The various sensations with which we subjectively feel our body and its parts are modifications of the fundamental feeling. The sentient soul, present throughout the body, furthermore perceives the changes produced "on the sensitive parts by the force of an external body": "the perception of this passivity that the sensitive soul undergoes in a given mode determined by the quality of the sensation is the sensitive perception of bodies" (ibid., a. 4). Sensation has an immanentistic meaning in the actualism (v.) of Gentile (v.). It is the initial and obscure moment from which the I begins the process toward its full spiritual reality as unity of subject and object, that is, as thought, self-consciousness: "Pure sensing, feeling, is therefore the principle in which thought, at its first dawn, and reality, in its deepest root, coincide" (Introd. alla filos., ch. 4, n. 20, Milan-Rome 1923, p. 87). "That ground, dark in itself but which he (the I) illuminates with his eternal self-making, that first point from which he takes his start in his eternal journey, the solid and unshakable base on which he, with his immanent activity, builds himself, and in himself all that determinate world which he in himself from hour to hour comes to determine — that is sense, which, seen from the outside, is the body, the physical world itself" (ibid., ch. 5, n. 20, pp. 107-108).

V. GNOSEOLOGICAL SIGNIFICANCE OF SENSATION

The idealistic conception, which understands s. as the first form of the immanent spontaneity of the spirit, grasps one of the authentic meanings of sensing, namely its character of activity and subjective transcendence. The s., through which the first forms of consciousness in act are posited, is lost in its essentiality if it is reduced to pure passivity, with the same meaning as the actions-reactions of the physical world. Against the materialistic reduction of sensing to a pure cosmic process (not overcome by the so-called "psycho-physical parallelism" of Wundt and others, which makes the fact of consciousness a simple "epiphenomenon" [v.] of the physiological fact), the interpretation of the s. as a moment of spiritual subjectivity is correct. In reality, the gradual determinations that sensing assumes in the unfolding and affirming of life in the world (from the extremely obscure "protopathic" sensibility of unicellular animals, which is barely a glimmer of "presence" and "awareness," to the complex critical differentiations it assumes at the summit of its perfection, in man), have their first source in the transcendence of the sentient subject that unfolds in multiple "forms" in living beings, and is posited, in man, as a spiritual principle, an ontological synthesis of sensing and thinking, of experience and self-consciousness. The s. is, in this way, the immediate manifestation of the presence of the sentient principle in a body individuated in time and space, and is determined in particular forms according to the structures of the sense organs and the action upon them of the physical world. Consequently, while it is posited as an immanent form of being of consciousness, the s. is at the same time, in various ways, according to the increasing degree of its qualitative differentiation, a revelation of the world, in the objective relations that the world itself assumes with the subject. The s. - like every intentional form of consciousness - is therefore neither pure subjectivity nor pure objectivity: on the contrary it expresses (and in this direction the interpretation and perceptionism [v.] seem to be reconciled) the determining of the physical world into "qualities" and "modes of representation" that have their formal principle in the expressive virtuality of the sentient principle, but are objectively conditioned - in their spatio-temporal meaning as "objects" and "things" - by the reality that becomes the physical stimulus of the organ. This accounts, on the one hand, for the characteristics of relativity of sensing (dependent principally on the "fluidity" of the conditions of the sense organs, and already clearly noted by Greek skepticism: cf. the "ten tropes" of Aenesidemus in Sextus Empiricus, Pyrrh. hypoth., I, § 14 ff.; v. SCETTICISMO) and, on the other, for the insuperable persuasion of objective reality and "transcendence" with which the s. is posited in human spiritual consciousness.

Wishing therefore to specify the gnoseological significance of the s., the following conclusions seem able to be accepted: a) Pure sensing, while positing itself as a form of cognitive presence, is a form of initial and obscure knowledge that does not realize a full opposition between object and subject, I and not-I.

b) The world of the s. does not resolve into itself, as phenomenism (v.) claims, entirely and without ontological residue, the world of reality; nor is it a simple reflection of a higher ideal reality (Plato). Not all aspects of the real are given in the s., which is only a partial representation of the world, in some of its physical dynamic characteristics. The realistic significance of the s. lies in its value as a transcription in terms of consciousness of real phenomena and activities of matter, and in its being conditioned by and proportioned to them.

c) As the first contact of consciousness with reality, the s. are moments in which being is given, albeit in an unapprehended manner (not as being, but in its concrete manifestations and physical activities). From this obscure giving of being in the s., the intelligence can proceed to the determination of the ontological ground on which the sensible object emerges and consists: moving in this direction it seeks the principles and causes of corporeal being (metaphysics). From the s. the intellect proceeds furthermore to the determination of sensible objects and of the s. themselves in their significance for the sentient subject: in this other direction the s. reveal their biological, existential, aesthetic, social, moral character (an ethical system, hedonism, resolves into the affective tone of the s. - pleasure, pain - moral values themselves, good-evil), and therefore also their essential function for man, a spirit incarnate in a sensible body, in relation to the attainment of particular ends and of the ultimate end of existence itself.

d) Pure s. as such, having no conceptual value, has no meaning of "certainty" either, in the gnoseological sense of the term. S. is therefore not evidence of reality, of being, of existence, but awareness of "modes," "affections," "qualities." Nevertheless, in man, through the unity of the sentient and intelligent principle (the s. in man almost never presents itself in a "pure" state) there is given with the s., in the judging consciousness, the presence of the concrete existing entity (in some modes and forms of its spatio-temporal activity). To the objects of the s. there therefore belongs a value of existence that nevertheless has different degrees: 1) There is a value of phenomenal-representative reality: it is proper to every object of s., but only insofar as it is "given," "represented": a weak reality, of the first degree, which also belongs to dreams, illusions, hallucinations, and to all the "false" representations of the senses. 2) A value of subjective-psychic reality: it is proper to every s. insofar as it is a psychic fact of the subject: an ontological but "subjective" and "accidental" reality. 3) A value of transsubjective, transcendent reality, according to which the object of the s. reveals itself as having an existence of its own in the physical world. Such reality, globally, is the intentional reference of all sensibility: through it the real "situation" of the sentient being (animal-man) in the world is explained and clarified; its existing with multiple relations of biological needs, necessity, dependence, on physical reality. But in relation to the individual objects of the s. the transcendent reality (and its degree) are not universally determined and must be established with the criterion of the "critical convergence" of the various sensory planes, and together by the more or less positive and effective function that an object of s. fulfills in relation to the existential necessities of the living being.

e) In pure s., as there is no formal evidence, so there is no formal truth or error: the s. is always determined by the encounter of an objective stimulus (external or internal) with the subjective conditions of sense and as such is neither true nor false. But, through the contingency of the conditions of the object and of the subject, the sensitive representation can, to varying degrees, fail to correspond to the conditions of reality in itself (limit cases: hallucinations, and in general representations from pathological affections of the organ): "sensum affici est ipsum sentire. Unde per hoc quod sensus ita nuntiant sicut afficiuntur, sequitur quod non decipiantur in iudicio quo iudicamus nos sentire aliquid. Sed ex hoc quod sensus aliter afficitur quam res sit, sequitur quod nobis nuntiant aliquando rem aliter quam sit" (Sum. Theol., 1°, q. 17, a. 2, c.). Such an intrinsic condition of sensibility does not entail a negative judgment on its value and positivity. Since, as St. Thomas also affirms, "naturas... sensibilium qualitatum intelligere non est sensus sed intellectus" (ibid., 1°, q. 78, a. 3, c.), to determine the positive significance and at the same time the limits of the s. as a revelation of being belongs to thought, in which finally the s. is clarified and defined as knowledge.

Ugo Viglino