When, considering visible objects, by which we ought to begin, we
combine one (being) with another, as for instance, a horse and a dog,
or two men, and say that they form two; or, when considering a greater
number of men we say they are ten, and form a group of ten, this number
does not constitute being, nor an (accident) among sense-objects; it is
purely and simply a quantity. Dividing this group of ten by unity, and
making unity of its parts, you obtain and constitute the principle of
quantity (unity) for a unity thus derived from a group of ten.