“Now, if he was forced to look directly at the firelight, wouldn’t his eyes be pained? Wouldn’t he turn away and run back to those things which he normally perceived and understand them as more defined and clearer than the things now being brought to his attention?”

Plato - Allegory of the Cave

“An afterlife would be a real possibility. Because of this fundamental uncertainty, even the basement civilization may have a reason to behave ethically. The fact that it has such a reason for moral behavior would of course add to everybody else’s reason for behaving morally, and so on, in truly virtuous circle. One might get a kind of universal ethical imperative, which it would be in everybody’s self‐interest to obey, as it were ‘from nowhere’” 

Nick Bostrom, Are you living in a computer simulation

“Thirty spokes converge on a hub but it's the emptiness that makes a wheel work // 
Pots are fashioned from clay but it's the hollow that make a pot work // Windows and doors are carved for a house but it's the spaces that make a house work // Existence makes something useful but nonexistence makes it work” 

Lao Tzu, Dao De king

“All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wise not to trust entirely to anything by which we have once been deceived” 

Descartes, Mediations on First Philosophy

“Then without a doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something. So that after having reflected well and carefully examined all things, we must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it”   

Descartes, Mediations on First Philosophy

“Whence then come my errors? They come from the sole fact that since the will is much wider in its range and compass than the understanding, I do not restrain it within the same bounds, but extend it also to things which I do not understand: and as the will is of itself indifferent to these, it easily falls into error and sin, and chooses the evil for the good, or the false for the true.” 

Descartes, Mediations on First Philosophy

“And although possibly (or rather certainly, as I shall say in a moment) I possess a body with which I am very intimately conjoined, yet because, on the one side, I have a clear and distinct idea of myself inasmuch as I am only a thinking and unextended thing, and as, on the other, I possess a distinct idea of body, inasmuch as it is only an extended and unthinking thing, it is certain that this I [that is to say, my soul by which I am what I am], is entirely and absolutely distinct from my body, and can exist without it.” 

Descartes, Mediations on First Philosophy

“Given that the soul of a human being is only a thinking substance, how can it affect the bodily spirits, in order to bring about voluntary actions? The question arises· because it seems that how a thing moves depends solely on (i) how much it is pushed, (ii) the manner in which it is pushed, or (iii) the surface-texture and shape of the thing that pushes it. The first two of those require contact between the two things, and the third requires that the causally active thing be extended. Your notion of the soul entirely excludes extension, and it appears to me that an immaterial thing can’t possibly touch anything else. So I ask you for a definition of the soul that homes in on its nature more thoroughly than does the one you give in your Meditations, i.e. I want one that characterizes what it is as distinct from what it does (namely to think).”   

Princess Elisabeth of Bohemia, Correspondents (letters to Descartes)

“If we consider a manufactured object, such as a book or a paper knife, we note that this object was produced by a craftsman who drew his inspiration from a concept: he referred both to the concept of what a paper knife is, and to a known production technique that is a part of that concept and is, by and large, a formula. The paper knife is thus both an object produced in a certain way and one that, on the other hand, serves a definite purpose. We cannot suppose that a man would produce a paper knife without knowing what purpose it would serve. Let us say, therefore, that the essence of the paper knife — that is, the sum of formulae and properties that enable it to be produced and defined — precedes its existence. Thus the presence before my eyes of that paper knife or book is determined.” 

Sartre, Existentialism is a Humanism

“Existentialism is not so much an atheism in the sense that it would exhaust itself attempting to demonstrate the nonexistence of God; rather, it affirms that even if God were to exist, it would make no difference —that is our point of view. It is not that we believe that God exists, but we think that the real problem is not one of his existence; what man needs is to rediscover himself and to comprehend that nothing can save him from himself, not even valid proof of the existence of God.” 

Sartre, Existentialism is a Humanism

“Some things are up to us and some are not up to us. Our opinions are up to us, and our impulses, desires, aversions—in short, whatever is our own doing. Our bodies are not up to us, nor are our possessions, our reputations, or our public offices, or, that is, whatever is not our own doing. The things that are up to us are by nature free, unhindered, and unimpeded; the things that are not up to us are weak, enslaved, hindered, not our own. So remember, if you think that things naturally enslaved are free or that things not your own are your own, you will be thwarted, miserable, and upset, and will blame both gods and men. But if you think that only what is yours is yours, and that what is not your own is, just as it is, not your own, then no one will ever coerce you, no one will hinder you, you will blame no one, you will not accuse anyone, you will not do a single thing unwillingly, you will have no enemies, and no one will harm you, because you will not be harmed at all”   

Epictetus, The Handbook of Epictetus

“What are the moral implications of a situation like this? In what follows, I shall argue that the way people in relatively affluent countries react to a situation like that in Bengal cannot be justified; indeed, the whole way we look at moral issues—our moral conceptual scheme —needs to be altered, and with it, the way of life that has come to be taken for granted in our society.” 

Peter Singer, Famine Affluence and Autonomy

“It follows from what I have said earlier that we ought to give money away, rather than spend it on clothes which we do not need to keep us warm. To do so is not charitable, or generous. Nor is it the kind of act which philosophers and theologians have called "supererogatory"—an act which it would be good to do, but not wrong not to do. On the contrary, we ought to give the money away, and it is wrong not to do so.” 

Peter Singer, Famine Affluence and Autonomy

“Man is a reasonable being; and as such, receives from science his proper food and nourishment: But so narrow are the bounds of human understanding, that little satisfaction can be hoped for in this particular, either from the extent of security or his acquisitions. Man is a sociable, no less than a reasonable being: But neither can he always enjoy company agreeable and amusing, or preserve the proper relish for them. Man is also an active being; and from that disposition, as well as from the various necessities of human life, must submit to business and occupation: But the mind requires some relaxation, and cannot always support its bent to care and industry. It seems, then, that nature has pointed out a mixed kind of life as most suitable to the human race, and secretly admonished them to allow none of these biases to draw too much, so as to incapacitate them for other occupations and entertainments.”   

David Hume, Enquiry Concerning Human Understanding

“A man of mild manners can form no idea of inveterate revenge or cruelty; nor can a selfish heart easily conceive the heights of friendship and generosity. It is readily allowed, that other beings may possess many senses of which we can have no conception; because the ideas of them have never been introduced to us in the only manner by which an idea can have access to the mind, to wit, by the actual feeling and sensation.” 

David Hume, Enquiry Concerning Human Understanding

“The most perfect philosophy of the natural kind only staves off our ignorance a little longer: As perhaps the most perfect philosophy of the moral or metaphysical kind serves only to discover larger portions of it. Thus the observation of human blindness and weakness is the result of all philosophy, and meets us, at every turn, in spite of our endeavours to elude or avoid it” 

David Hume, Enquiry Concerning Human Understanding

“Hume in the end transforms the concept of reason.  From being a quasi-divine faculty, something we share with God, reason becomes a natural capacity and one that is essentially shared with those who learn from experience in the way we do, sharing expressive body language, sharing or able to share a language, sharing or able to share our sentiments, sharing or able to share intellectual, moral, and aesthetic standards, and sharing or aspiring to share in the setting of those standards.” 

Annette Baier, Hume The Reflective Women’s Epistemologist

“Our evidence, then, for the truth of the Christian religion is less than the evidence for the truth of our senses; because, even in the first authors of our religion, it was no greater; and it is evident it must diminish in passing from them to their disciples; nor can any one rest such confidence in their testimony, as in the immediate object of his senses. But a weaker evidence can never destroy a stronger; and therefore, were the doctrine of the real presence ever so clearly revealed in scripture, it were directly contrary to the rules of just reasoning to give our assent to it.” 

David Hume, Enquiry Concerning Human Understanding

“As the soul is immortal, has been born often, and has seen all things here and in the underworld, there is nothing which it has not learned; so it is in no way surprising that it can recollect the things it knew before, both about virtue and other things. As the whole of nature is akin, and the soul has learned everything, nothing prevents a man, after recalling one thing only—a process men call learning—discovering everything else for himself, if he is brave and does not tire of the search, for searching and learning are, as a whole, recollection.”   

Plato, Meno

“For true opinions, as long as they remain, are a fine thing and all they do is good, but they are not willing to remain long, and they escape from a man’s mind, so that they are not worth much until one ties them down by (giving) an account of the reason why. And that, Meno, my friend, is recollection, as we previously agreed. After they are tied down, in the first place they become knowledge, and then they remain in place. That is why knowledge is prized higher than correct opinion, and knowledge differs from correct opinion in being tied down." 

Plato, Meno

“The word ‘love’ is most often defined as a noun, yet all the more astute theorist of love acknowledge that we would all love better if we used it as a verb. Echoing the work of Erich Fromm, [Peck] defines love as ‘the will to extend oneself for the purpose of nurturing one’s own or another’s spiritual growth.’ Explaining further, he continues: ‘Love is as love does. Love is an act of will—namely, both an intention and an action. Will also implies choice. We do not have to love. We choose to love.’ Since the choice must be made to further growth, this definition counters the more widely accepted assumption that we love instinctually.” 

Bell Hooks, All About Love

“Definitions are vital starting points for the imagination. What we cannot imagine cannot come into being. A good definition marks our starting point and lets us know where we want to end up” 

Bell Hooks, All About Love