White and sweet are perceived by two distinct senses, and at two distinct moments of time; but they must be compared and discriminated by one and the same sentient or cogitant act, and at one moment of time.[110] This mental act, though in itself indivisible, has yet two aspects, and is thus in a certain sense divisible; just as a point taken in the middle of a line, while indivisible in itself, may be looked upon as the closing terminus of one-half of the line, and as the commencing terminus of the other half. The comparison of two different sensations or thoughts is thus one and the same mental fact, with two distinguishable aspects.[111]
[110] Aristot. De Animâ, III. ii. p. 426, b. 17-29: οὔτε δὴ κεχωρισμένοις ἐνδέχεται κρίνειν ὅτι ἕτερον τὸ γλυκὺ τοῦ λευκοῦ, ἀλλὰ δεῖ ἑνί τινι ἄμφω δῆλα εἶναι. — δεῖ δὲ τὸ ἓν λέγειν ὅτι ἕτερον· ἕτερον γὰρ τὸ γλυκὺ τοῦ λευκοῦ. — ἀχώριστον καὶ ἐν ἀχωρίστῳ χρόνῳ. III. vii. p. 431, a. 20.
[111] Aristot. De Animâ, III. ii. p. 427, a. 10-14: ὥσπερ ἣν καλοῦσί τινες στιγμήν, ᾗ μιὰ καὶ ᾗ δύο, ταύτῃ καὶ ἀδιαίρετος καὶ διαιρέτη· ᾗ μὲν οὖν ἀδιαίρετον, ἓν τὸ κρῖνόν ἐστι καὶ ἅμα, ᾗ δὲ διαίρετον ὑπάρχει, οὐχ ἕν· δὶς γὰρ τῷ αὐτῷ χρῆται σημείῳ ἅμα.
It is to be remarked that, in explaining this mental process of comparison, Aristotle three several times applies it both to αἴσθησις and to νόησις, p. 426, b. 22-31; p. 427, a. 9.
Aristotle devotes a chapter to the enquiry: whether we can perceive two distinct sensations at once (i.e. in one and the same moment of time). He decides that we cannot; that the sentient soul or faculty is one and indivisible, and can only have a single energy or actuality at once.[112] If two causes of sensation are operative together, and one of them be much superior in force, it will render us insensible to the other. He remarks that, when we are pre-occupied with loud noise, or with deep reflection, or with intense fright, visual objects will often pass by us unseen and unnoticed.[113] Often the two simultaneous sensations will combine or blend into one compound, so that we shall feel neither of them purely or separately.[114] One single act of sensational energy may however have a double aspect; as the same individual object may be at once white and sweet, though its whiteness and its sweetness are logically separable.[115]
[112] Aristot. De Sensu et Sensili, vii. p. 447, a. 12.
[113] Ibid. a. 15.
[114] Ibid. b. 12-20.
[115] Ibid. p. 449, a. 14.
To the sentient soul, even in its lowest manifestations, belong the feelings of pleasure and pain, appetite and aversion.[116] The movements connected with these feelings, as with all sensation, begin and close with the central organ — the heart.[117] Upon these are consequent the various passions and emotions; yet not without certain faculties of memory and phantasy accompanying or following the facts of sense.