In a complete thought or mental proposition, all the members and parts are mutually related, some slightly, some more intimately. In communicating such a thought, it is not sufficient that the component ideas be clearly expressed: it is also necessary, that all the relations contained in the thought be expressed according to their different degrees of intimacy. To annex a certain meaning to a certain sound or word, requires no art. The great nicety in all languages is, to express the various relations that connect together the parts of the thought. Could we suppose this branch of language to be still a secret, it would puzzle, I am apt to think, the greatest grammarian ever existed, to invent an expeditious method. And yet, by the guidance merely of nature, the rude and illiterate have been led to a method so perfect, that it appears not susceptible of any improvement. Without a clear conception of the manner of expressing relations, one at every turn must be at a loss about the beauties of language; and upon that subject therefore I find it necessary to say a few words.
Words that import a relation, must be distinguished from those that do not. Substantives commonly imply no relation, such as _animal_, _man_, _tree_, _river_. Adjectives, verbs, and adverbs, imply a relation. The adjective _good_ must be connected with some substantive, some being possessed of that quality. The verb _write_ must be applied to some person who writes; and the adverbs _moderately_, _diligently_, have plainly a reference to some action which they modify. When in language a relative term is introduced, all that is necessary to complete the expression, is, to ascertain that thing to which the term relates. For answering this purpose, I observe in Greek and Latin two different methods. Adjectives are declined as well as substantives; and declension serves to ascertain the connection that is betwixt them. If the word that expresses the subject be, for example, in the nominative case, so also must the word be that expresses its quality. Example, _vir bonus_. Again, verbs are related, on the one hand, to the agent; and, on the other, to the subject upon which the action is exerted. A contrivance similar to that now mentioned, serves to express this double relation. The nominative case is appropriated to the agent, the accusative to the passive subject; and the verb is put in the first second or third person, to correspond the more intimately with both. Examples: _Ego amo Tulliam_; _tu amas Semproniam_; _Brutus amat Portiam_. The other method is by juxtaposition, which is necessary with respect to words only that are not declined, adverbs for example, articles, prepositions, and conjunctions. In the English language there are few declensions; and therefore juxtaposition is our chief resource. Adjectives accompany their substantives[89]; an adverb accompanies the word it qualifies; and the verb occupies the middle place betwixt the active and passive subjects to which it relates.