T 2.3.3.4

Since reason alone can never produce any action, or give rise to volition, I infer, that the same faculty is as incapable |of preventing volition, or of disputing the preference with any passion or emotion. This consequence is necessary. 'Tis impossible reason cou'd have the latter effect of preventing volition, but by giving an impulse in a contrary direction to our passion; and that impulse, had it operated alone, wou'd have been able to produce volition. Nothing can oppose or retard the impulse of passion, but a contrary impulse; and if this contrary impulse ever arises from reason, that latter faculty must have an original influence on the will, and must be able to cause, as well as hinder any act of volition. But if reason has no original influence, 'tis impossible it can withstand any principle, which has such an efficacy, or ever keep the mind in suspence a moment. Thus it appears, that the principle, which opposes our passion, cannot be the same with reason, and is only call'd so in an improper sense. We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them. As this opinion may appear somewhat extraordinary, it may not be improper to confirm it by some other considerations.