from the PensÃ©es
taken from Bill Wood Words and Ideas Webpage.
Knowledge has two extremes which meet; one is the pure natural ignorance of every man at birth, the other is the extreme reached by great minds who run through the whole range of human knowledge, only to find that they know nothing and come back to the same ignorance from which they set out, but it is a wise ignorance which knows itself. [V.83]
There is no certainty, apart from faith, as to whether man was created by a good God, an evil demon, or just by chance, and so it is a matter of doubt, depending on our origin, whether these principles are true, false or uncertain.
Moreover, no one can be sure, apart from faith, whether he is sleeping or waking, because when we are asleep we are just as firmly convinced that we are awake as we are now. As we often dream we are are dreaming, piling up one dream on another, is it not possible that this half of our life is itself just a dream, on to which others are grafted and from which we shall awake when we die? . . . [VIII.136]
It is absurd of us to rely on the company of our fellows, as wretched and helpless as we are; they will not help us; we shall die alone.
We must act then as if we were alone. If that were so, would we build superb houses, etc.? We should unhesitatingly look for the truth. And, if we refuse, it shows we have a higher regard for men's esteem than for pursuing the truth. [XII.151]
There is nothing so consistent with reason as this denial of reason. [XIII.182]
The whole visible world is only an imperceptible dot in nature's ample bosom. No idea comes near it; it is no good inflating our conceptions beyond imaginable space, we only bring forth atoms compared to the reality of things. Nature is an infinite sphere whose center is everywhere and circumference nowhere. In short it is the greatest perceptible mark of God's omnipotence that our imagination should lose itself in that thought. [XV.199]
The heart has its order, the mind has its own, which uses principles and demonstrations. The heart has a different one. We do not prove that we ought to be loved by setting out in order the causes of love; that would be absurd. [XXIII.298]
The heart has its reasons of which reason knows nothing: we know this in countless ways. 
Men are so inevitably mad that not to be mad would be to give a mad twist to madness.