18. Consequences of words, and consequences of ideas. Though the deducing one proposition from another, or making inferences in words, be a great part of reason, and that which it is usually employed about; yet the principal act of ratiocination is the finding the agreement or disagreement of two ideas one with another, by the intervention of a third. As a man, by a yard, finds two houses to be of the same length, to measure their equality by juxta-position. Words have their consequences, as the signs of such ideas: and things agree or disagree, as really they are; but we observe it only by our ideas.
19. Four sorts of arguments. Before we quit this subject, it may be worth our while a little to reflect on four sorts of arguments, that men, in their reasonings with others, do ordinarily make use of to prevail on their assent; or at least to awe them as to silence their opposition.
I. Argumentum ad verecundiam. The first is, to allege the opinions of men, whose parts, learning, eminency, power, or some other cause has gained a name, and settled their reputation in the common esteem with some kind of authority. When men are established in any kind of dignity, it is thought a breach of modesty for others to derogate any way from it, and question the authority of men who are in possession of it. This is apt to be censured, as carrying with it too much pride, when a man does not readily yield to the determination of approved authors, which is wont to be received with respect and submission by others: and it is looked upon as insolence, for a man to set up and adhere to his own opinion against the current stream of antiquity; or to put it in the balance against that of some learned doctor, or otherwise approved writer. Whoever backs his tenets with such authorities, thinks he ought thereby to carry the cause, and is ready to style it impudence in any one who shall stand out against them. This I think may be called argumentum ad verecundiam.
20. II. Argumentum ad ignorantiam. Secondly, Another way that men ordinarily use to drive others and force them to submit to their judgments, and receive their opinion in debate, is to require the adversary to admit what they allege as a proof, or to assign a better.
And this I call argumentum ad ignorantiam.
21. III. Argumentum ad hominem. Thirdly, a third way is to press a man with consequences drawn from his own principles or concessions.
This is already known under the name of argumentum ad hominem.
22. IV. Argumentum adjudicium. The fourth alone advances us in knowledge and judgment. The fourth is the using of proofs drawn from any of the foundations of knowledge or probability. This I call argumentum adjudicium. This alone, of all the four, brings true instruction with it, and advances us in our way to knowledge. For, 1. It argues not another man's opinion to be right, because I, out of respect, or any other consideration but that of conviction, will not contradict him. 2. It proves not another man to be in the right way, nor that I ought to take the same with him, because I know not a better. 3. Nor does it follow that another man is in the right way because he has shown me that I am in the wrong. I may be modest, and therefore not oppose another man's persuasion: I may be ignorant, and not be able to produce a better: I may be in an error, and another may show me that I am so. This may dispose me, perhaps, for the reception of truth, but helps me not to it: that must come from proofs and arguments, and light arising from the nature of things themselves, and not from my shamefacedness, ignorance, or error.
23. Above, contrary, and according to reason. By what has been before said of reason, we may be able to make some guess at the distinction of things into those that are according to, above, and contrary to reason. 1. According to reason are such propositions whose truth we can discover by examining and tracing those ideas we have from sensation and reflection; and by natural deduction find to be true or probable. 2. Above reason are such propositions whose truth or probability we cannot by reason derive from those principles. 3.
Contrary to reason are such propositions as are inconsistent with or irreconcilable to our clear and distinct ideas. Thus the existence of one God is according to reason; the existence of more than one God, contrary to reason; the resurrection of the dead, above reason.
Above reason also may be taken in a double sense, viz. either as signifying above probability, or above certainty: and in that large sense also, contrary to reason, is, I suppose, sometimes taken.