Key Arguments

• Senses can misrepresent objects, as in perceptual illusions (e.g., jaundice makes all appear yellow; distant bodies appear smaller).
• Clear sensory appearances (like the sun’s apparent size) do not license judgments about reality without rational assessment.
• Vivid imagination (e.g., conceiving a chimaera) does not entail real existence.
• Dreams can present thoughts as lively and distinct as waking experiences, so vividness alone is not a criterion of truth; reason must adjudicate.

Source Quotes

in the same manner when awake; as when persons in the jaundice see all objects yellow, or when the stars or bodies at a great distance appear to us much smaller than they are. For, in fine, whether awake or asleep, we ought never to allow ourselves to be persuaded of the truth of anything unless on the evidence of our reason. And it must be noted that I say of our reason, and not of our imagination or of our senses: thus, for example, although we very clearly see the sun, we ought not therefore to determine that it is only of the size which our sense of sight presents; and we may very distinctly imagine the head of a lion joined to the body of a goat, without being therefore shut up to the conclusion that a chimaera exists; for it is not a dictate of reason that what we thus see or imagine is in reality existent; but it plainly tells us that all our ideas or notions contain in them some truth; for otherwise it could not be that God, who is wholly perfect and veracious, should have placed them in us.

For, in fine, whether awake or asleep, we ought never to allow ourselves to be persuaded of the truth of anything unless on the evidence of our reason. And it must be noted that I say of our reason, and not of our imagination or of our senses: thus, for example, although we very clearly see the sun, we ought not therefore to determine that it is only of the size which our sense of sight presents; and we may very distinctly imagine the head of a lion joined to the body of a goat, without being therefore shut up to the conclusion that a chimaera exists; for it is not a dictate of reason that what we thus see or imagine is in reality existent; but it plainly tells us that all our ideas or notions contain in them some truth; for otherwise it could not be that God, who is wholly perfect and veracious, should have placed them in us. And because our reasonings are never so clear or so complete during sleep as when we are awake, although sometimes the acts of our imagination are then as lively and distinct, if not more so than in our waking moments, reason further dictates that, since all our thoughts cannot be true because of our partial imperfection, those possessing truth must infallibly be found in

Key Concepts

• we ought never to allow ourselves to be persuaded of the truth of anything unless on the evidence of our reason.
• it must be noted that I say of our reason, and not of our imagination or of our senses
• although we very clearly see the sun, we ought not therefore to determine that it is only of the size which our sense of sight presents
• we may very distinctly imagine the head of a lion joined to the body of a goat, without being therefore shut up to the conclusion that a chimaera exists
• it is not a dictate of reason that what we thus see or imagine is in reality existent

Context

Part 4, continuing the response to dream skepticism and sensory error, reinforcing the rule that only reason provides grounds for assent.