Thirdly, We may now be able fully to overcome all that repugnance, which it is so natural for us to entertain against the foregoing reasoning, by which we endeavoured to prove, that the necessity of a cause to every beginning of existence is not founded on any arguments either demonstrative or intuitive.  Such an opinion will not appear strange after the foregoing definitions.  If we define a cause to be an object precedent and contiguous to another, and where all the objects resembling the farmer are placed in a like relation of .priority and contiguity to those objects, that resemble the latter; we may easily conceive, that there is no absolute nor metaphysical necessity, that every beginning of existence should be attended with such an object.  If we define a cause to be, an object precedent and contiguous to another, and so united with it in the imagination, that the idea of the one determines the mind to form the idea of the other, and the impression of the one to form A more lively idea of the other; we shall make still less difficulty of assenting to this opinion.  Such an influence on the mind is in itself perfectly extraordinary and incomprehensible; nor can we be certain of its reality, but from experience and observation.

I shall add as a fourth corrollary that we can never have reason to believe that any object exists, of which we cannot form an idea.  For as all our reasonings concerning existence are derived from causation, and as all our reasonings concerning causation are derived from the experienced conjunction of objects, not from any reasoning or reflection, the same experience must give us a notion of these objects, and must remove all mystery from our conclusions.  This is so evident, that it would scarce have merited our attention, were it not to obviate certain objections of this kind, which might arise against the following reasonings concerning matter and substance.  I need not observe, that a full knowledge of the object is not requisite, but only of those qualities of it, which we believe to exist.

SECT.  XV.  RULES BY WHICH TO JUDGE OF CAUSES AND EFFECTS.

According to the precedent doctrine, there are no objects which by the mere survey, without consulting experience, we can determine to be the causes of any other; and no objects, which we can certainly determine in the same manner not to be the causes.  Any thing may produce any thing.  Creation, annihilation, motion, reason, volition; all these may arise from one another, or from any other object we can imagine.  Nor will this appear strange, if we compare two principles explained above, that the constant conjunction of objects determines their causation, and [Part I. Sect. 5.] That, property speaking, no objects are contrary to each other but existence and non-existence.  Where objects are not contrary, nothing hinders them from having that constant conjunction, on which the relation of cause and effect totally depends.