as a possibility in the mind, meaning that he does not know it to be impossible, not as a possibility in external reality, meaning that he knows it to be possible in external reality.
There is a difference between knowing something to be possible and not knowing it to be impossible. Many people confuse the two. When someone conceives of something he does not know to be impossible, or is asked about it, he says:
“This is possible; this is not impossible; supposing it to exist would entail no impossibility.”
If he is asked:
“Your statement, ‘Supposing it to exist would entail no impossibility,’ is a universal proposition and a general negation. How, then, do you know that supposing it to exist would entail no impossibility? Someone who denies a claim must provide evidence, just as someone who affirms it must provide evidence. Did you know this through self-evident knowledge shared by rational people, through reasoning shared by them, through self-evident knowledge peculiar to you, or through reasoning peculiar to you? If it was through shared self-evident knowledge, your rational peers would necessarily share this knowledge with you. Yet that is not how they see the matter.
“If it was through shared reasoning, where is the evidence that you and they share? If it was through self-evident knowledge or reasoning peculiar to you, this too is invalid, for two reasons.
“First, you claim that this is something rational people share, that they must agree with you on it, and that, if they debated with you, this argument would leave them unable to reply. That precludes your claiming that this knowledge is peculiar to you.
“Second, such knowledge could be peculiar to you, whether self-evident or acquired through reasoning, only if you possessed something that warranted this distinction—as with someone singled out for prophethood, a particular experience, or something else peculiar to him. Yet this is not your situation concerning what you claim to be possible.
“Nor do you claim that knowledge of its possibility is peculiar to you. Even if you make such a claim, others are not obliged to agree with you on this if you do not present