36. There are two ways, and there are only two, in which differences arise. These are, 1°, the _modes of production_ of a product, and, 2°, our _modes of apprehension_ of the product. Things may be very different, and yet to our apprehension indistinguishable, so that we regard them as identical; and they may be identical, yet appear utterly unlike. A mechanical bird may seem so like a living bird, and their actions so indistinguishable to the spectator, that he will not suspect a difference, or suspecting it, will not be able to specify it. Of both objects, so long as his modes of apprehending them are circumscribed, he can only say what these imply: he sees familiar forms, colors, and movements, which he interprets according to the previous experiences of which these are the signs. But by varying the modes of apprehension, and gaining thus a fuller knowledge, he finds that the two products have very different modes of production; hence he concludes the products to be different: the mechanism of the one is not the organism of the other; the actions of the mechanical bird are not the actions of the living bird. The fuller knowledge has been gained by viewing the objects under different relations, and contemplating them _in_ their modes of production, not as merely visible products. He sees the mechanism performing by steel springs, wheels, and wires, the work which the organism performs by bones, muscles, and nerves; and the farther his analysis of the modes of production is carried, the greater are the differences which he apprehends.