Neither the true nor the false roots are always real; sometimes they are imaginary; that is, while we can always imagine as many roots for each equation as I have assigned, yet there is not always a definite quantity corresponding to each root we have imagined.

There is nothing more ancient than the truth.

We never understand a thing so well,and make it our own, as when we have discovered it for ourselves.

There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.

Just as we believe by faith that the greatest happiness of the next life consists simply in the contemplation of this divine majesty, likewise we experience that we derive the greatest joy of which we are capable in this life from the same contemplation, even though it is much less perfect.

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.

Now therefore, that my mind is free from all cares, and that I have obtained for myself assured leisure in peaceful solitude, I shall apply myself seriously and freely to the general destruction of all my former opinions.