(of purposes) can also be thought, which regarded as a series would lead either forwards or backwards; in this the thing that has been called the effect may with equal propriety be termed the cause of that of which it is the effect.

In the practical department of human art we easily find connexions such as this; e.g. a house, no doubt, is the cause of the money received for rent, but also conversely the representation of this possible income was the cause of building the house. Such a causal connexion we call that of final causes (nexus finalis). We may perhaps suitably name the first the connexion of real causes, the second of those which are ideal; because from this nomenclature it is at once comprehended that there can be no more than these two kinds of causality.