Aristotle admits, with Plato, of final and efficient causes. These efficient causes are sensitive and vegetative souls, that give form to matter which, of itself, is only a capacity of receiving forms; and as in generation the female gives the most abundant matter, and it being against his system of final causes to admit that what one could effect should be performed by many, he concludes, that the female alone contains the necessary matter to generation; and, as another of his principles was, that matter itself is unformed, and that form is a distinct being from matter, he affirmed that the male furnished the form, and, consequently, nothing belonging to matter. Descartes, on the contrary, who admitted but a few mechanical principles in his philosophy, endeavoured to explain the formation of the foetus by them, and thought it in his power to comprehend, and make others understand, how an organized and living being could be made by the laws of motion alone. His admitted principles differed from those used by Aristotle; but both, instead of examining the thing itself, without prepossession and prejudice, have only considered it in the point of view relative to their systems of philosophy, which could not be attended with a successful application to the nature of generation, because it depends, as we have shewn, on quite different principles. Descartes differs still more from Aristotle, by admitting of the mixture of the seminal liquor of the two sexes; he thinks both furnish something material for generation, and that the fermentation occasioned by the mixture of these two seminal liquors causes the formation of the foetus.