What challenges or counter-arguments might arise if one were to solely base moral judgments on "sentiment" as opposed to "reason," and how might Hume address these?

From the book

ble of like impressions. The only way, therefore, of converting an antagonist of this kind, is to leave him to himself. For, finding that nobody keeps up the controversy with him, it is probable he will, at last, of himself, from mere weariness, come over to the side of common sense and reason. There has been a controversy started of late, much better worth examination, concerning the general foundation of Morals; whether they be derived from Reason, or from Sentiment; whether we attain the knowledge of them by a chain of argument and induction, or by an immediate feeling and finer…

e a SENTIMENT should here display itself, in order to give a preference to the useful above the pernicious tendencies. This SENTIMENT can be no other than a feeling for the happiness of mankind, and a resentment of their misery; since these are the different ends which virtue and vice have a tendency to promote. Here therefore REASON instructs us in the several tendencies of actions, and HUMANITY makes a distinction in favour of those which are useful and beneficial. This partition between the faculties of understanding and sentiment, in all moral decisions, seems clear from the…

leasure. No man reasons concerning another's beauty; but frequently concerning the justice or injustice of his actions. In every criminal trial the first object of the prisoner is to disprove the facts alleged, and deny the actions imputed to him: the second to prove, that, even if these actions were real, they might be justified, as innocent and lawful. It is confessedly by deductions of the understanding, that the first point is ascertained: how can we suppose that a different faculty of the mind is employed in fixing the other? On the other hand, those who would resolve all moral…

truth, while it keeps wholly in generals, makes use of undefined terms, and employs comparisons, instead of instances. This is particularly remarkable in that philosophy, which ascribes the discernment of all moral distinctions to reason alone, without the concurrence of sentiment. It is impossible that, in any particular instance, this hypothesis can so much as be rendered intelligible, whatever specious figure it may make in general declamations and discourses. Examine the crime of INGRATITUDE, for instance; which has place, wherever we observe good-will, expressed and known,…

interests which may be proposed; these, on many occasions, are doubtful, and subject to great discussion and inquiry. The object of municipal laws is to fix all the questions with regard to justice: the debates of civilians; the reflections of politicians; the precedents of history and public records, are all directed to the same purpose. And a very accurate REASON or JUDGEMENT is often requisite, to give the true determination, amidst such intricate doubts arising from obscure or opposite utilities. But though reason, when fully assisted and improved, be sufficient to instruct us in…