_Synderesis_ is an habitual hold upon primary moral judgments, as, that we must do good, avoid evil, requite benefactors, honour superiors, punish evil-doers. There is a hot controversy as to how these primary moral judgments arise in the mind. The coals of dispute are kindled by the assumption, that these moral judgments must needs have a totally other origin and birth in the mind than speculative first principles, as, that the whole is greater than the part, that two and two are four, that things which are equal to the same thing are equal to one another. The assumption is specious, but unfounded. It looks plausible because of this difference, that moral judgments have emotions to wait upon them, speculative judgments have not. Speculative judgments pass like the philosophers that write them down, unheeded in the quiet of their studies. But moral judgments are rulers of the commonwealth: they are risen to as they go by, with majesty preceding and cares coming after. Their presence awakens in us certain emotions, conflicts of passion, as we think of the good that we should do, but have not done, or of the evil that goes unremedied and unatoned for. Commonly a man cannot contemplate his duty, a difficult or an unfulfilled duty especially, without a certain emotion, very otherwise than as he views the axioms of mathematics. There is a great difference emotionally, but intellectually the two sets of principles, speculative and moral, are held alike as necessary truths, truths that not only are, but must be, and cannot be otherwise: truths in which the _predicate_ of the proposition that states them is contained under the _subject_. Such are called _self-evident propositions_; and the truths that they express, _necessary truths_. The enquiry into the origin of our primary moral judgments is thus merged in the question, how we attain to necessary truth. 6. The question belongs to Psychology, not to Ethics: but we will treat it briefly for ethical purposes. And first for a clear notion of the kind of judgments that we are investigating.