Branch of philosophy that deals with the first principles of things, including being, personhood, cause, agency, identity, time, and space.

David Hume on Cause and Effect


This deficiency in our ideas is not, indeed, perceived in common life, nor are we sensible, that in the most usual conjunctions of cause and effect we are as ignorant of the ultimate principle, which binds them together, as in the most unusual and extraordinary. But this proceeds merely from an illusion of the imagination; and the question is, how far we ought to yield to these illusions. This question is very difficult, and reduces us to a very dangerous dilemma, whichever way we answer it. For if we assent to every trivial suggestion of the fancy; beside that these suggestions are often contrary to each other; they lead us into such errors, absurdities, and obscurities, that we must at last become asham’d of our credulity. Nothing is more dangerous to reason than the flights of the imagination, and nothing has been the occasion of more mistakes among philosophers. Men of bright fancies may in this respect be compar’d to those angels, whom the scripture represents as covering their eyes with their wings. This has already appear’d in so many instances, that we may spare ourselves the trouble of enlarging upon it any farther.

Aristotle Presaging the Cogito and Categorical Imperative


Now, the good man has the same relation to his friend as he has to himself; for a friend is another self; in the same manner, therefore, as to exist one’s self is eligible to every one, so also is it for one’s friend to exist, or nearly so. But existence was said to be eligible on account of the perception of that which is a good: and such a perception is pleasant in itself. We ought, therefore, to be conscious of the existence of our friend; and this would result from associating with him, and sharing his words and thoughts; for this would seem to be the meaning of the word society, when applied to men, and not, as in the case of cattle, the merely feeding in the existence. If, then, existence is in itself eligible to the happy man, being by nature something good and pleasant, and if the existence of a friend is nearly the same, then a friend must also be of the number of eligible things. But that which is eligible to a man, he ought to possess; or else he is deficient in that respect; he, therefore, that is to be happy will need good friends.