these perceptions.  These observations are contrary, unless I suppose that the door still remains, and that it was opened without my perceiving it:  And this supposition, which was at first entirely arbitrary and hypothetical, acquires a force and evidence by its being the only one, upon which I can reconcile these contradictions.  There is scarce a moment of my life, wherein there is not a similar instance presented to me, and I have not occasion to suppose the continued existence of objects, in order to connect their past and present appearances, and give them such an union with each other, as I have found by experience to be suitable to their particular natures and circumstances.  Here then I am naturally led to regard the world, as something real and durable, and as preserving its existence, even when it is no longer present to my perception.

But though this conclusion from the coherence of appearances may seem to be of the same nature with our reasonings concerning causes and effects; as being derived from custom, and regulated by past experience; we shall find upon examination, that they are at the bottom considerably different from each other, and that this inference arises from the understanding, and from custom in an indirect and oblique manner.  For it will readily be allowed, that since nothing is ever really present to the mind, besides its own perceptions, it is not only impossible, that any habit should ever be acquired otherwise than by the regular succession of these perceptions, but also that any habit should ever exceed that degree of regularity.  Any degree, therefore, of regularity in our perceptions, can never be a foundation for us to infer a, greater degree of regularity in some objects, which are not perceived; since this supposes a contradiction, viz. a habit acquired by what was never present to the mind.  But it is evident, that whenever we infer the continued existence of the objects of sense from their coherence, and the frequency of their union, it is in order to bestow on the objects a greater regularity than what is observed in our mere perceptions.  We remark a connexion betwixt two kinds of objects in their past appearance to the senses, but are not able to observe this connexion to be perfectly constant, since the turning about of our head or the shutting of our eyes is able to break it.  What then do we suppose in this case, but that these objects still continue their usual connexion, notwithstanding their apparent interruption, and that the irregular appearances are joined by something, of which we are insensible?  But as all reasoning concerning matters of fact arises only from custom, and custom can only be the effect of repeated perceptions, the extending of custom and reasoning beyond the perceptions can never be the direct and natural effect of the constant repetition and connexion, but must arise from the co-operation of some other principles.