I. Hylas and Philonous encounter one another in the garden (p. 580).

A. Philonous remarks on the sensory qualities of their experience.

B. Hylas confesses that he is vexed by skepticism and skeptics. Philonous agrees and Hylas is surprised and relieved, since Philonous had been characterized as someone who denies material substance.

C. Philonous admits that he does deny material substance.

II. H&P discuss the meaning of 'skeptic'. They settle on this: someone who "denies the reality of sensible things or professes the greatest ignorance of them" (p. 581).

III. H&P discuss 'sensible things' (p. 581).

A. Sensible things are things perceived by the senses.

B. Things perceived by the senses are perceived immediately.

1. Immediate perception is contrasted with mediate perception, i.e., when that which is perceived is a means to something else.

a. Specifically, the cause of things perceived by the senses are not perceived by the senses. Hylas proposes that "deducing therefore of causes...entirely relates to reason" (p. 582).

C. Question — Does the reality of sensible things consist in their being perceived or in something else?

1. Hylas's Answer — To be perceived is one thing, to exist is another.

IV. Discussion of Heat (p. 582).

A. Hylas claims that whatever degree of heat is perceived in a thing, that degree of heat exists as real in that thing.

1. Philonous claims that great heat is the same as great pain, and Hylas agrees.

a. Problem for Hylas's view — Great pain cannot exist in a thing, since pain is had only by things with minds.

b. Hylas takes back his agreement that great heat is great pain and claims instead that the pain is a consequence of the heat.

i. Problem for Hylas's view — We do not perceive two things, both the heat and the pain. Therefore, the two cannot be distinct (as far as sensible properties are concerned).

ii. Hylas takes back his claim that whatever degree of heat is perceived in a thing, that degree of heat exists as real in that thing for the case of great heat. He continues to maintain his thesis for less heat.

B. H&P repeat the above discussion in the case of warmth. Philonous claims that warmth is a pleasure, Hylas ultimately claims that it is the privation of pleasure or pain. Philonous disagrees, but moves on.

C. H&P repeat the above discussion in the case of cold and come to the same conclusions.

V. Methodological point — Any doctrine that leads to absurdity must be rejected (p. 584).

1. Contradictions are the premiere example of absurdity.

VI. An extended discussion of perceptual relativity arguments (PRA) begins (p. 584).

A. Sketch of the strategy — Two hands in a bucket of water.

B. Tastes

1. Philonous mentions that sweetness is a kind of pleasure, but pleasures cannot be in sugar.

2. Philonous gives a PRA for the claim that sweetness is not in sugar. Namely, he works from the thesis that people taste things differently.

C. Odors

D. Sounds (This is not, strictly speaking, a PRA. We may view it as an interlude.)

1. Hylas enthusiastically claims that sound is in the air. He knows this because science tells him so.

a. Philonous claims that sound and air motion always occur together, but that that does not show that sound is in the air.

b. Philonous points out that if sound is a sensation, then it cannot be in the air.

c. Philonous points out that the way we talk about sound — as loud or acute — is not appropriate to air.

i. Hylas distinguishes between real sound and what the 'vulgar' think sound is.

d. Philonous points out that, on Hylas's view, the way we hear sounds is by our sense of touch.

E. Colors

1. Hylas claims that objects have the colors that we perceive in them.

a. Philonous asks whether the clouds are red and purple as they appear, or are dark mist and vapor.

i. Hylas distinguishes between real and apparent color.
ii. Philonous asks how we are to decide which colors are real.
iii. Hylas proposes nearness as a gauge of real color.
iv. Philonous claims that this absurd.

2. Hylas claims that colors are light. H&P replicate their discussion of sounds, above.

a. Hylas offers the distinction between primary and secondary qualities.

F. Extension

1. Hylas claims that extension is in the object.

a. Philonous gives PRA's against both size and texture.

G. Motion

1. Philonous claims that motion is a function of time over space.

2. Philonous claims that time is the succession of ideas.

3. Philonous gives a PRA against the real existence of motion.

H. Solidity

1. Philonous gives a PRA against the real existence of solidity.

VII. H&P attempt to diagnose why the primary quality/secondary quality distinction seems to compelling (p. 590).

VIII. Hylas suggests absolute extension, i.e., extension abstracted from size or shape (p. 590).

A. Philonous proposes that everything that exists is particular.

1. Philonous claims that abstract ideas are inconceivable.

2. Hylas proposes that perhaps pure intellect can conceive of abstract ideas.

a. Philonous says he has no idea what Hylas is talking about.

IX. Hylas distinguishes object and sensation by claiming that sensations involve an act of mind, while objects are not an act of mind (p. 592).

A. Philonous proposes that an act of mind can only occur by act of will.

1. Philonous claims that sensations do not involve an act since they do not involve acts of will.

X. Hylas claims that there is a material substratum underlying his sensations (p. 593).

A. Philonous asks by what sense is the material substratum perceived.

1. Hylas agrees that it is the product of reflection and reason. Specifically, it is postulated relationally.

a. Philonous challenges Hylas to specify the nature of the material substratum.

i. Infinite regress of extension

XI. Hylas attempts to conceive of something unperceived by any mind whatsoever (p. 594).

A. Philonous claims that this is absurd, since Hylas is perceiving that which he conceives.

1. Hylas is embarrassed.