33. The Common Sense and Discrimination Between Sensibles

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Lecture Notes

Main Topics #

• The Discrimination Problem: How we distinguish sensible objects from different senses (white vs. sweet) when no single external sense knows both
• The Common Sense: Aristotle’s introduction of an inward sense power that must be singular in number to judge sensible differences
• Simultaneous Reception: How the common sense receives impressions from all external senses at the same undivided time
• The Unity Problem: Whether a single power can receive contraries or multiple sensibles without them excluding each other
• Inward vs. Outward Experience: How we know the common sense through inward experience of discrimination, and how outward dissection might confirm this

Key Arguments #

The Impossibility of External Senses Alone #

• Each external sense discriminates only within its own proper sensible: sight distinguishes colors, taste distinguishes flavors
• Sight cannot know sweetness; taste cannot know whiteness
• Therefore, neither sense alone can judge that white and sweet are different things
• Even two senses together cannot make this judgment unless a single power knows both objects

The Analogy to Syllogism #

• If person A knows only the major premise and person B knows only the minor premise, neither can syllogize alone
• Example: “Every mother is a woman” (known by A) and “No man is a woman” (known by B) cannot yield “No man is a mother” unless one person knows both premises
• Similarly, to discriminate between white and sweet, one power must know both sensibles
• Analogy extends to spelling: if person A knows only ‘C’, person B knows only ‘A’, and person C knows only ‘T’, no one person can spell “cat” alone

The Nature of the Common Sense #

• It is one in number but multiple in definition (like a geometric point that is both the end of one line and the beginning of another)
• It must judge the difference at the same undivided time (not separated by temporal distance)
• The “now” of the knowing is not the same as the “now” of the known—contrast with memory, where we remember the past as past
• It is still within the order of sensation, not yet intellection

Important Definitions #

Common Sense (Central Sense) / Σὺν-αἴσθησις: An inward sense power that receives impressions from all external senses and judges their differences. Called “central” to distinguish it from “common sense” meaning practical judgment and from “common sensibles” (shape, motion, number).

Private/Proper Sensible / ἴδια αἰσθητά: The object proper to each single sense (color for sight, sound for hearing, flavor for taste).

Sensible in Potency / δυνάμει: The ability of an object to be sensed before it is actually sensed.

Sensible in Act / ἐνεργείᾳ: The actual affecting of a sense by its object; when the sensible is operating upon the sense.

Examples & Illustrations #

The Licorice Example #

One simultaneously perceives the blackness of licorice through sight and its taste through taste, and judges these two sensible qualities to be different—all through sensation, not reason’s abstract understanding.

The Syllogism Analogy #

Two premises distributed across two people: Person A knows “every mother is a woman” but not “no man is a woman.” Person B knows the latter but not the former. Neither can conclude “no man is a mother” alone. One person must possess both premises in their mind to make the inference.

The Point Analogy (Geometric) #

The common sense is like a geometric point that is:

• One in number (a single point)
• The endpoint of one line and the starting point of another simultaneously
• Yet actually one and the same point

This illustrates how the common sense can be unified while receiving multiple sensible impressions from different external senses.

The Multiplication Analogy #

If one person knows the number 4 but not 6, and another knows 6 but not 4, they cannot multiply 4 × 6 together. One person must hold both numbers in mind to calculate the product (24).

Questions Addressed #

Can One Power Receive Multiple Sensibles Without Confusion? #

• The common sense is not like matter, which cannot be acted upon by contraries simultaneously
• White and sweet are not true contraries in the same order, so they do not exclude each other
• The common sense, like a point, is immaterial enough to receive multiple impressions unified

Why Must Discrimination Occur at an Undivided Time? #

• If the common sense judged white and sweet at different times, it would be like remembering the past—the temporal gap would separate the objects
• For true discrimination (saying these two things are different right now), both must be present in consciousness simultaneously
• The “now” belongs to the act of knowing, not to the sensibles themselves

How Does Inward Experience Reveal the Common Sense? #

• We know the common sense through our direct experience of discriminating between white and sweet
• Outward dissection of the head might reveal physical connections between external senses and a central region (brain), confirming this inward knowledge
• Some truths are knowable only by inward experience; others only by outward observation; some by both

How Is the Common Sense Distinguished from Reason? #

• Reason compares the essences and definitions of things (what is sound, what is color)
• The common sense merely compares the sensible qualities themselves (the sound, the color) without understanding what they are
• Both can compare objects of different senses, but they operate at different levels of abstraction

Context and Method #

Berquist emphasizes that Aristotle’s treatment in these passages is based on common, inward experience—the same foundation as the eight books of natural philosophy rest on common experience of natural things. The argument proceeds from what we directly experience (our ability to discriminate white from sweet) to the necessary conditions that make this experience possible (an inward, unified sense power).

The lecture also notes that Thomas Aquinas, in other texts, argues more strongly than Aristotle that even the perception of sensory acts themselves (like seeing the act of seeing) requires an inward sense, though Aristotle does not force this conclusion as clearly.