Il est bon de savoir quelque chose des moeurs de divers peuples, afin de juger des nôtres plus sainement, et que nous ne pensions pas que tout ce qui… - René Descartes

The passions, then, can be defined as ‘perceptions, or sensations, or emotions of the soul that we refer (rapportons) particularly to the soul itself, and that are caused, sustained, and fortified by some movement of the spirits’ (§27).

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

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.