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'.
To this objection experience will perhaps be found to furnish the true answer. We find in fact that we cannot compare two objects till we have passed and repassed them in the mind.
'Supposing this account of the operation of the mind in comparison to be admitted， yet what shall we say to a complex sentence， containing twenty ideas， the sense of which I fully apprehend at a single hearing， nay， even， in some cases， by the time one half of it has been uttered？'
The mere talk of understanding what is affirmed to us is of a very different nature from that of comparison， or of any other species of judgment that is to be formed concerning this affirmation. When a number of ideas are presented in a train， though in one sense there be variety， yet in another there is unity. First， there is the unity of uninterrupted succession， the perennial flow as of a stream， where the drop indeed that succeeds is numerically distinct from that--which went before， but there is no cessation.
Secondly， there is the unity of method， The mind apprehends， as the discourse proceeds， a strict association from similarity or some other source， between each idea： as it follows in the process， and that which went before it.
The faculty of understanding the different parts of a discourse in their connection with each other， simple as it appears， is in reality of gradual and slow acquisition. We are， by various causes， excluded from a minute observation of the progress of the infant mind， and therefore do not readily conceive by how imperceptible advances it arrives at a quickness of apprehension， relative to the simplest sentences. But we more easily remark its subsequent improvement， and perceive how long it is， before it can apprehend a discourse of considerable length， or a sentence of great abstraction.
Nothing is more certain than the possibility of my perceiving the sort of relation that exists between the different parts of a methodical discourse， for example， Mr Burke's Speech upon Oeconomical Reform， though it be impossible for me， after the severest attention， to consider the several parts otherwise than successively. I have a latent feeling of this relation as the discourse proceeds， but I cannot give a firm judgement respecting it， otherwise than by retrospect. It may however be suspected， even in the case of simple apprehension， that an accurate attention to the operations of the mind would show that we scarcely in any instance hear a single sentence without returning again and again upon the steps of the speaker and drawing more closely in our minds the preceding members of his period， before he arrives at its conclusion； though even this exertion of mind， subtle as it is， be not of itself thought sufficient to authorize us to give a judgement of the whole.
But， if the principle here stated be true， how infinitely rapid must be the succession of ideas？ While I am speaking， no two ideas are in my mind at the same time， and yet with what facility do I pass from one to another？ If my discourse be argumentative， how often do I pass in review the topics of which it consists， before I utter them； and， even while I第一章m speaking， continue the review at intervals， without producing any pause in my discourse？ How many other sensations are experienced by me during this 'period， without so much as interrupting， that is， without materially diverting the train of my ideas？ My eye successively remarks a thousand objects that present themselves. My mind wanders to the different parts of my body， and receives a sensation from the chair upon which I sit， or the table upon which I lean； from the pinching of a shoe， from a singing in my ear， a pain in my head， or an irritation of the breast. When these most perceptibly occur， my mind passes from one to another without feeling，the minutest obstacle， or being in any degree distracted by their multiplicity.