Page:Essays on the Principles of Human Action (1835).djvu/168

 Not that it is possible for colour or motion to exist without extension, but only that the mind can frame to itself by abstraction the idea of colour, exclusive of extension, and of motion exclusive both of colour and extension. Again, the mind having observed that in the particular extensions perceived by sense, there is something common and alike in all, and some other things peculiar, as this or that figure, or magnitude, which distinguish them one from another, it considers apart, or singles out by itself that which is most common, making thereof a most abstract idea of extension, line, surface, or solid, nor has any figure or magnitude, but is an idea prescinded from all these. So likewise the mind by leaving out of the particular colours perceived by sense, that which distinguishes them one from another, and retaining that which only is common to all, makes an idea of colour in abstract, which is neither red, nor blue, nor white, &c. And in like manner by considering motion abstractedly, not only the body moved, but likewise from the figure it describes, and all particular directions and velocities, the abstract idea of motion is framed, which equally corresponds to all particular motions whatsoever that may be perceived by sense.

And as the mind frames to itself abstract ideas of qualities, or modes, so does it by the precision or mental separation, attain abstract ideas of the more compound beings, which include several co-existent qualities:–for example, the mind having observed, that Peter, James, John, &c. resemble each other in certain common agreements of shape, and other qualities, leaves out of the complex or compounded idea it has of Peter, James, &c. that which is peculiar to each, retaining only what is common to all; and so makes an abstract idea wherein the particulars equally partake, abstracting entirely, and cutting off all