There are two kinds of questions, some belonging to the first causes, the others have only particular effects; for example, if it is asked, why matter is impenetrable? it must either remain unanswered, or be replied to by saying, matter is impenetrable, because it is impenetrable. It will be the same with respect to all the general qualities of matter, whether relative to gravity, extension, motion or rest; no other reply can be given, and we shall not be surprised that such is the case, if we attentively consider, that in order to give a reason for a thing, we must have a different subject from which we may deduce a comparison, and therefore if the reason of a general cause is asked, that is, of a quality which belongs to all in general, and of which we have no subject to which it does not belong, we are consequently unable to reason upon it; from thence it is demonstrable, it would be useless to make such enquiries, since we should go against the supposition that quality is general and universal. If, on the contrary, the reason of a particular effect depends immediately on one of the general causes above mentioned, and whether it partakes of the general effect immediately, or by a chain of other effects, the question will be equally solved, provided we distinctly perceive the dependence these effects have on each other, and the connections there are between them. But if the particular effect, of which we enquire the reason, does not appear to depend on these general effects, nor to have any analogy with other known effects, then this effect, being the only one of its kind, and having nothing in common with other effects, at least known to us, the question is insolvable: because, not having, in this point, any known subject which has any connection with that we would explain, there is nothing from whence we can draw the reason sought after. When the reason of a general cause is demanded, it is unanswerable, because it exists in every object; and, on the other hand, the reason of a singular or isolated effect is not found, because not any thing known has the same qualities. We cannot explain the reason of a general effect, without discovering one more general; whereas the reason of an isolated effect may be explained by the discovery of some other relative effect, which although we are ignorant of at present, chance or experience may bring to light. Besides these, there is another kind of question, which may be called, the question of fact. For example. Why do trees, dogs, &c. exist? All these fact questions are totally insoluble, for those who answer them by final causes do not consider that they take the effect for the cause; the connection particular objects have with us having no influence on their origin. Moral affinity can never become a physical reason.