One cannot conceive anything so strange and so implausible that it has not already been said by one philosopher or another.
It is only prudent never to place complete confidence in that by which we have even once been deceived.
An optimist may see a light where there is none, but why must the pessimist always run to blow it out?
It's the familiar love-hate syndrome of seduction: "I don't really care what it is I say, I care only that you like it."
Any community that gets its laughs by pretending to be idiots will eventually be flooded by actual idiots who mistakenly believe that they're in good company.
When I consider this carefully, I find not a single property which with certainty separates the waking state from the dream. How can you be certain that your whole life is not a dream?
I was convinced that our beliefs are based much more on custom and example than on any certain knowledge.
Each problem that I solved became a rule, which served afterwards to solve other problems.
For I found myself embarrassed with so many doubts and errors that it seemed to me that the effort to instruct myself had no effect other than th eincreasing discovery of my own ignorance
Conquer yourself rather than the world.
The only secure knowledge is that I exist.
Doubt is the origin of wisdom
The reading of all good books is like a conversation with the finest minds of past centuries.
The greatest minds are capable of the greatest vices as well as of the greatest virtues.
The chief cause of human errors is to be found in the prejudices picked up in childhood.
If I simply refrain from making a judgment in cases where I do not perceive the truth with sufficient clarity and distinctness, then it is clear that I am behaving correctly and avoiding error.
Divide each difficulty into as many parts as is feasible and necessary to resolve it.
If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.
Truths are more likely to be discovered by one man than by a nation
By 'God', I understand, a substance which is infinite, independent, supremely intelligent, supremely powerful, and which created both myself and everything else [...] that exists. All these attributes are such that, the more carefully I concentrate on them, the less possible it seems that they could have originated from me alone. So, from what has been said it must be concluded that God necessarily exists
Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them. I realized that it was necessary, once in the course of my life, to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last.
Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.
We do not describe the world we see, we see the world we can describe.
It is not enough to have a good mind; the main thing is to use it well.
There is nothing more ancient than the truth.
Illusory joy is often worth more than genuine sorrow.
I can doubt everything, except one thing, and that is the very fact that I doubt. Simply put - I think, therefore I am
Intuitive knowledge is an illumination of the soul, whereby it beholds in the light of God those things which it pleases Him to reveal to us by a direct impression of divine clearness.
The only thing that I know, is that I know nothing
Human wisdom remains always one and the same although applied to the most diverse objects and it is no more changed by their diversity than the sunshine is changed by the variety of objects which it illuminates.
For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it.
This result could have been achieved either by his [God] endowing my intellect with a clear and distinct perception of everything about which I would ever deliberate, or simply by impressing the following rule so firmly upon my memory that I could never forget it: I should never judge anything that I do not clearly and distinctly understand.
The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.
But possibly I am something more than I suppose myself to be.
Every man is indeed bound to do what he can to promote the good of others, and a man who is of no use to anyone is strictly worthless.
You just keep pushing. You just keep pushing. I made every mistake that could be made. But I just kept pushing.
The principal effect of the passions is that they incite and persuade the mind to will the events for which they prepared the body.
Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency.