An interesting passage may be quoted from [393] Plutarch on the Stoic doctrine of knowledge: "The Stoics maintain," he says, "that when a human being is born, he has the governing part of his soul like a sheet of paper ready prepared for the reception of writing, and on this the soul inscribes in succession its various ideas. The first form of the writing is produced through the senses. When we perceive, for example, {232} a white object, the recollection remains when the object is gone. And when many similar recollections have accumulated, we have what is called _experience_. Besides the ideas which we get in this natural and quite undesigned way, there are other ideas which we get through teaching and information. In the strict sense only these latter ought to be called ideas; the former should rather be called perceptions. Now the rational faculty, in virtue of which we are called reasoning beings, is developed out of, or over and beyond, the mass of perceptions, in the second seven years' period of life. In fact a thought may be defined as a kind of mental image, such as a rational animal alone is capable of having." Thus there are various gradations of mental apprehensions; first, those of sensible qualities obtained through the action of the objects and the assent of the perceiving subject, as already described; then by experience, by comparison, by analogy, by the combinations of the reasoning faculty, further and more general notions are arrived at, and conclusions formed, as, for example, that the gods exist and exercise a providential care over the world. By this faculty also the wise man ascends to the apprehension of the good and true.