No more useful inquiry can be proposed than that which seeks to determine the nature and the scope of human knowledge. ... This investigation should … - René Descartes

There is such a strong connection between body and soul that thoughts that accompanied certain movements of our body at the beginning of our lives, go on accompanying them later.

porque también pueden los sentidos engañarnos con frecuencia durante la vigilia, como los que tienen ictericia lo ven todo amarillo, o

Thus, all unknown quantities can be expressed in terms of a single quantity, whenever the problem can be constructed by means of circles and straight lines, or by conic sections, or even by some other curve of degree not greater than the third or fourth.
But I shall not stop to explain this in more detail, because I should deprive you of the pleasure of mastering it yourself, as well as of the advantage of training your mind by working over it, which is in my opinion the principal benefit to be derived from this science. Because, I find nothing here so difficult that it cannot be worked out by anyone at all familiar with ordinary geometry and with algebra, who will consider carefully all that is set forth in this treatise.