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.