It is impossible there can be a progress IN INFINITUM; and that one thing can always be a reason why another is desired.

Something must be desirable on its own account, and because of its immediate accord or agreement with human sentiment and affection.
Now as virtue is an end, and is desirable on its own account, without fee and reward, merely for the immediate satisfaction which it conveys; it is requisite that there should be some sentiment which it touches, some internal taste or feeling, or whatever you may please to call it, which distinguishes moral good and evil, and which embraces the one and rejects the other.
Thus the distinct boundaries and offices of REASON and of TASTE are easily ascertained.

The former conveys the knowledge of truth and falsehood: the latter gives the sentiment of beauty and deformity, vice and virtue.

The one discovers objects as they really stand in nature, without addition and diminution: the other has a productive faculty, and gilding or staining all natural objects with the colours, borrowed from internal sentiment, raises in a manner a new creation.

Reason being cool and disengaged, is no motive to action, and directs only the impulse received from appetite or inclination, by showing us the means of attaining happiness or avoiding misery: Taste, as it gives pleasure or pain, and thereby constitutes happiness or misery, becomes a motive to action, and is the first spring or impulse to desire and volition.