equality, coincidence, truth, and in some cases, those of utility, importance, &c.
For mathematical propositions are, in some cases, attended with a practical assent, in the proper sense of these words; as when a person takes this or that method of executing a projected design, in consequence of some mathematical proposition assented to from his own examination, or on the authority of others. Now, that which produces the train of voluntary actions, here denoting the practical assent, is the frequent recurrency of ideas of utility and importance. These operate according to the method laid down in the 20th proposition, i.e. by association; and though the rational assent be a previous requisite, yet the degree of the practical assent is proportional to the vividness of these ideas; and in most cases they strengthen the rational assent by a reflex operation.
Propositions concerning natural bodies are of two kinds, vulgar and scientifical. Of the first kind are, that milk is white, gold yellow, that a dog barks, &c. These are evidently nothing but forming the present complex idea belonging to material objects into a proposition, or adding some of its common associates, so as to make it more complex. There is scarce room for dissent in such propositions, they being all taken from common appearances. Or, if any doubt should arise, the matter must be considered scientifically. The assent given to these propositions arises from the associations of the terms, as well as of the ideas denoted by them.
In scientifical propositions concerning natural bodies, a definition is made, as of gold from its properties, suppose its colour, and specific gravity, and another property or power joined to them, as a constant or common associate. Thus gold is said to be ductile, fixed, or soluble in aqua regia. Now to persons who have made the proper experiments a sufficient number of times, these words suggest the ideas which occur in those experiments, and, conversely, are suggested by them, in the same manner as the vulgar propositions above-mentioned suggest and are suggested by common appearances. But then, if they be scientifical persons, their readiness to affirm that gold is soluble in aqua regia universally, arises also from the experiments of others, and from their own and others’ observations on the constancy and tenor of nature. They know, that the colour, and specific gravity, or almost any two or three remarkable qualities of any natural body, infer the rest, being never found without them. This is a general truth; and as these general terms are observed to coincide, in fact, in a great variety of instances, so they coincide at once in the imagination, when applied to gold, or any other natural body, in particular. The coincidence of general terms is also observed to infer that of the particular cases in many instances, besides those of natural bodies; and this unites the subject and predicate of the proposition, gold is
