And those whose hearts are fixed on Reality itself deserve the title of Philosophers.
When the mind's eye rests on objects illuminated by truth and reality, it understands and comprehends them, and functions intelligently; but when it turns to the twilight world of change and decay, it can only form opinions, its vision is confused and its beliefs shifting, and it seems to lack intelligence.
What is at issue is the conversion of the mind from the twilight of error to the truth, that climb up into the real world which we shall call true philosophy.
The society we have described can never grow into a reality or see the light of day, and there will be no end to the troubles of states, or indeed, my dear Glaucon, of humanity itself, till philosophers are kings in this world, or till those we now call kings and rulers really and truly become philosophers, and political power and philosophy thus come into the same hands. (Plato, Republic, 380BC)
It is clear, then, that wisdom is knowledge having to do with certain principles and causes. But now, since it is this knowledge that we are seeking, we must consider the following point: of what kind of principles and of what kind of causes is wisdom the knowledge?
Finally, if nothing can be truly asserted, even the following claim would be false, the claim that there is no true assertion. (Aristotle, ~340BC)
She (philosophy) is equally helpful to the rich and poor: neglect her, and she equally harms the young and old. (Horace)
Since philosophy is the art which teaches us how to live, and since children need to learn it as much as we do at other ages, why do we not instruct them in it? (de Montaigne)
It is a good thing to proceed in order and to establish propositions. This is the way to gain ground and to progress with certainty. ... I hold that the mark of a genuine idea is that its possibility can be proved, either a priori by conceiving its cause or reason, or a posteriori when experience teaches us that it is in fact in nature.
But it is the knowledge of necessary and eternal truths which distinguishes us from mere animals, and gives us reason and the sciences, raising us to knowledge of ourselves and God. It is this in us which we call the rational soul or mind. (Gottfried Leibniz, Philosophical Investigations, 1670)
Philosophy being nothing else but the study of wisdom and truth, it may with reason be expected, that those who have spent most time and pains in it should enjoy a greater calm and serenity of mind, a greater clearness and evidence of knowledge, and be less disturbed with doubt and difficulties than other men. Yet so it is we see the illiterate bulk of mankind that walk the high-road of plain, common sense and are governed by the dictates of nature, for the most part easy and undisturbed. ... But no sooner do we depart from sense and instinct to follow the light of a superior principle, to reason, meditate and reflect on the nature of things, but a thousand scruples spring up in our minds, concerning those things which before we seemed fully to comprehend. Prejudices and errors of sense do from all parts discover themselves to our view; and endeavouring to correct these by reason we are insensibly drawn into uncouth paradoxes, difficulties, and inconsistencies, which multiply and grow upon us as we advance in speculation; till at length, having wandered through many intricate mazes, we find ourselves just where we were, or, which is worse, sit down in a forlorn scepticism. ... My purpose therefore is, to try if I can discover what those principles are, which have introduced all that doubtfulness and uncertainty, those absurdities and contradictions into the several sects of philosophy; insomuch that the wisest men have thought our ignorance incurable, conceiving it to arise from the natural dullness and limitation of our faculties. (George Berkeley, 1710)
And though the philosopher may live remote from business, the genius of philosophy, if carefully cultivated by several, must gradually diffuse itself throughout the whole society, and bestow a similar correctness on every art and calling. The politician will acquire greater foresight and subtlety, in the subdividing and balancing of power; the lawyer more method and finer principles in his reasoning; and the general public more regularity in his discipline, and more caution in his plans and operations. (David Hume, 1737)
It is the duty of philosophy to destroy the illusions which had their origin in misconceptions, whatever darling hopes and valued expectations may be ruined by its explanations. My chief aim in this work has been completeness; and I make bold to say, that there is not a single metaphysical problem that does not find its solution, or at least the key to its solution, here. Pure reason is a perfect unity. (Immanuel Kant, Critique of Pure Reason, 1781)
The philosophers have merely interpreted the world in various ways; the point, however, is to change it. (Karl Marx)
Greek philosophy seems to begin with a preposterous fancy, with the proposition (of Thales) that water is the origin and mother-womb of all things. Is it really necessary to stop there and become serious? Yes, and for three reasons: firstly, because the proposition does enunciate something about the origin of things; secondly, because it does so without figure and fable; thirdly and lastly, because it contained, although only in the chrysalis state, the idea :everything is one. ..That which drove him (Thales) to this generalization was a metaphysical dogma, which had its origin in a mystic intuition and which together with the ever renewed endeavors to express it better, we find in all philosophies - the proposition: everything is one! (Friedrich Nietzsche, 1890)
All our philosophy is dry as dust if it is not immediately translated into some act of living service. (Mohandas Gandhi)
In my opinion, the greatest scandal of philosophy is that, while all around us the world of nature perishes - and not the world of nature alone - philosophers continue to talk, sometimes cleverly and sometimes not, about the question of whether this world exists. They get involved in scholasticism, in linguistic puzzles such as, for example, whether or not there are differences between 'being' and 'existing'. ... But should there exist something like the correspondence of a theory to the facts, then this would obviously be more important than mere self-consistency, and certainly also more important than coherence with any earlier 'knowledge' (or 'belief'); for if a theory corresponds to the facts but does not cohere with some earlier knowledge, then this earlier knowledge should be discarded. (Karl Popper, 1975)