ject or perfon, any more than we can conceive a fourth dimenfion of body.

Let it be observed too, that those three canons are of the nature of axioms. They are self-evident neceffary truths, bearing that relation to the notion of conftant conjunction, which the axioms of geometry bear to the notion of quantity; and if the former notion, as well as the latter, be admitted to be juft, they are axioms to all intents and purposes.

SECT. VII.

Illuftrations of the exact import of the reafonings in the preceding fection.-Inftances of the truth of the inferences from the principle of Conftant Conjunction in cafes of Caufe and Effect in Phyfics; and of the plaufibility of them in many cafes of the relation of Motive and Action.

T

'Hough I regard the reasoning in the preceding fection as perfectly fatiffactory and unquestionable; yet I am far from thinking that this fuperfedes the neceffity of illuftrating it very fully for though both the subject and the reafoning be fufficiently fimple, yet it must be owned, that they are both very abftrufe, and no common, and confequently no easy, objects of attention. But I think they may be explained and illustrated by proper stances, in fuch a manner, that a child of

in

ten

ten years of age, of ordinary capacity, fhall eafily and fully understand them. Indeed little more is required to enable a perfon to understand them, than that he fhould understand or should be capable of learning arithmetical addition and subtraction.

It is plain, in the first place, that either caufes or motives may be applied fingly; and if the conjunction of caufe and effect and that of motive and action be constant, every cause or motive fingly applied will be followed by its proper effect or action.

Thus, a body will move from impulse, melt with heat, or diffolve in its proper menftruum; and a man will eat because he is hungry, drink because he is thirsty, run away because he is afraid, do kind actions from benevolence, and commit cruel and unjust actions from anger, malice, or rapacity. And this is expressed by the fimple formula X A, Y=B, &c.

In the fecond place, it is equally plain, that different caufes or motives may be conjoined, that is to fay, may concur in producing one kind of effect, or in prompting to one kind of action; and a greater effect or action of that kind will be produced by fuch a concurrence of caufes or motives, than by any one of them fingly applied.

Thus, a fhip under fail with a favourable wind, will move with a certain velocity; and with a greater, if at the fame time fhe is in a favourable current; and with a greater ftill, if at the fame time she is taken in tow by a fhip that fails faster than fhe does; or if the is impelled by the force of oars, when these can be used. And a man who will do a good deal from a fenfe of duty, and more from duty and honour and intereft conjoined, will do still more when there is fuperadded to these motives the terror of military discipline. This case of the application of causes or motives, and the neceffary refult of it, according to the principle affu

med,

med, is expreffed by the first canon, X+

Y=A+B.

In the third place, it must be evident, that either caufes or motives may be directly opposed by other caufes or other motives. If the oppofite caufes or motives are of unequal force or strength, the more powerful will prevail.

!

Thus, a fhip will advance against an adverse current, if the velocity in one direction which the acquires from the wind is greater than what she would acquire in the oppofite direction, from the current. And a foldier will face any danger in the way of his profeffion, if his sense of duty, of honour, of intereft, or even his dread of punishment, are with him stronger motives than fear of the enemy; but he will run away, if this fear be the stronger motive.

If the oppofite caufes or motives are equal, then they will exactly balance each other, like equal weights in the oppofite fcales of a juft balance; or like a fhip un

der