The same confusion may also be caused by lack of uniform force in the images and from other analogous causes, which there is no need to discuss here, the consideration of one cause being sufficient for the purpose we have in view. For it all comes to this, that these terms signify ideas in the highest degree confused. It is in this way that those notions have arisen which are called _Universal_, such as, _Man_, _Horse_, _Dog_, etc.; that is to say, so many images of men, for instance, are formed in the human body at once, that they exceed the power of the imagination, not entirely, but to such a degree that the mind has no power to imagine the determinate number of men and the small differences of each, such as color and size, etc. It will therefore distinctly imagine that only in which all of them agree in so far as the body is affected by them, for by that the body was chiefly affected, that is to say, by each individual, and this it will express by the name _man_, covering thereby an infinite number of individuals; to imagine a determinate number of individuals being out of its power. But we must observe that these notions are not formed by all persons in the same way, but that they vary in each case according to the thing by which the body is more frequently affected, and which the mind more easily imagines or recollects. For example, those who have more frequently looked with admiration upon the stature of men, by the name _man_ will understand an animal of erect stature, while those who have been in the habit of fixing their thoughts on something else, will form another common image of men, describing man, for instance, as an animal capable of laughter, a biped without feathers, a rational animal, and so on; each person forming universal images of things according to the temperament of his own body. It is not therefore to be wondered at that so many controversies have arisen amongst those philosophers who have endeavored to explain natural objects by the images of things alone. _The Three Kinds of Knowledge_ From what has been already said, it clearly appears that we perceive many things and form universal ideas: 1. From individual things, represented by the senses to us in a mutilated and confused manner, and without order to the intellect. These perceptions I have therefore been in the habit of calling knowledge from vague experience. 2. From signs; as, for example, when we hear or read certain words, we recollect things and form certain ideas of them similar to them, through which ideas we imagine things. These two ways of looking at things I shall hereafter call knowledge of the first kind, opinion or imagination. 3. From our possessing common notions and adequate ideas of the properties of things. This I shall call reason and knowledge of the second kind.