“But not to omit anything it is necessary to know, I shall briefly add something about the causes from which the terms called Transcendental have their origin – I mean terms like Being, Thing, and Something. These terms arise from the fact that the human body, being limited, is capable of forming distinctly only a certain number of images at the same time (I have explained what an image is in P17S). If that number is exceeded, the images will begin to be confused, and if the number of images the body is capable of forming distinctly in itself at once is greatly exceeded, they will all be completely confused with one another.
Since this is so, it is evident from P17C and P18, that the human mind will be able to imagine distinctly, at the same time, as many bodies as there can be images formed at the same time in it body. But when the images in the body are completely confused, the mind also will imagine all the bodies confusedly, without any distinction, and comprehend them as if under one attribute, namely, under the attribute of Being, Thing, and so forth. This can be deduced from the fact that images are not always equally vigorous and from other causes like these, which it is not necessary to explain here. For our purposes it is sufficient to consider only one. For they all reduce to this: these terms signify ideas that are confused in the highest degree.
Those notions they call Universal, like Man, Horse, Dog, and the like, have arisen from similar causes, namely, because so many images (e.g. of men) are formed at one time in the human body that they surpass the power of imagining – not entirely, of course, but still to the point where the mind can imagine neither slight differences of the singular [men] (such as the color and size of each one, etc.) nor their determinate number, and imagines distinctly only that they all agree in, insofar as they [NS: forcefully] by [what is common], since each singular has affected it [by this property]. And [NS: the mind] expresses this by the word man, and predicated it of infinitely many singulars. For as we have said, it cannot imagine a determinate number of singulars.
But it should be noted that these notions are not formed by all [NS: men] in the same way, but vary from one to another, in accordance with what the body has more often been affected by, and what the mind imagines or recollects more easily. For example, those who have more often regarded men’s stature with wonder will understand by the word man an animal of erect stature. But those who have been accustomed to consider something else will form another common image of men – for example, that man is an animal capable of laughter, or a featherless biped, or a rational animal.”
P40, part II. Of the Mind, Ethics, 1677 – Benedict De Spinoza