We shall later see many instances of this tendency of relations to make us ·wrongly· identify different objects with one another, but here I shall stay with the present subject. We find by experience that there is so much constancy in most of the impressions of the senses that their interruption produces no alteration in them, allowing them to returning ·to our senses· with the same appearance and situation as they had before. I survey the furniture in my room; I shut my eyes and then re-open them; and I find my new perceptions to resemble perfectly the previous ones. I observe this resemblance ·across interruptions· in a thousand instances, and it naturally connects my ideas of these interrupted perceptions by the strongest relation, conveying the mind easily from one to another. An easy passage of the imagination along the ideas of these •different and interrupted perceptions is almost the same disposition of mind as that in which we contemplate •one constant and uninterrupted perception. It is therefore very natural for us to mistake the one for the other.8
8This reasoning is admittedly rather abstruse and hard to understand; but the remarkable fact is that this very difficulty can be turned into an argument for the reasoning! We can see that there are two resemblances that contribute to our mistaking •the sequence of our interrupted perceptions for •an identical object. The first is the resemblance of the perceptions that are involved in each; the second is the resemblance of the acts of the mind that are involved in each. Now we are apt to confound these resemblances with each other, ·and that is what makes this whole piece of theory hard to get straight in one’s mind·. It is also what it is natural for us to do, according to this very theory. If you can only keep the two resemblances distinct, you’ll have no difficulty in following my argument.