747. 'Two and two' means complementary things. This may become clear to anyone from the fact that they are pairs. It is impossible for them to be pairs unless they are complementary to one another as truths and goods are, or evils and falsities. In fact all things contain the likeness of a marriage or a coupling together, as in the case of truths to goods, or of evils to falsities, because of the marriage of the understanding to the will, or of things of the understanding to those of the will. Indeed everything contains a marriage or coupling together of its own on which its very continuance depends.