The true answer to this objection seems to be as follows. The mind can apprehend only a single idea at once， but that idea needs not be a simple idea. The mind can apprehend two or more objects at a single effort， but it cannot apprehend them as two. There seems no sufficient reason to deny that all those objects which are painted at once upon the retina of the eye produce a joint and simultaneous impression upon the mind. But they are not immediately conceived by the mind as many， but as one： the recollection may occur that they are made up of parts， but these parts cannot be considered by us otherwise than successively. The resolution of objects into their simple elements is an operation of science and improvement； but it is altogether foreign to our first and original conceptions. In all cases， the operations of our understanding are rather analytical than synthetical， rather those of resolution than composition. We do not begin with the successive perception of elementary parts till we have obtained an idea of a whole； but beginning with a whole， are capable of reducing it into its elements.
A second difficulty is of a much subtler nature. It consists in the seeming 'impossibility of performing any mental operation， such as comparison for example， which has relation to two or more ideas， if we have not both ideas before us at once， if one of them be completely vanished and gone， before the other begins to exit'. The source of this difficulty seems to lie in the mistake of supposing that there is a real interval between the two ideas. It will perhaps be found upon an accurate examination that， though we cannot have two ideas at once， yet it is not just to say that the first has perished， before the second begins to exist. The instant that connects them is of no real magnitude， and produces no real division.
The mind is always full. It is this instant therefore that is the true point of comparison.
It may be objected 'that comparison is rather a matter of retrospect， deciding between two ideas that have been completely apprehended， than a perception which occurs in the middle， before the second has been observed'.