One of the commonest omissions in argumentation is to take the precedent for granted. This is allowable when it is a fact universally known or believed. 'If you let the glass fall it will be broken,'--the omitted precedent is the known consequences of letting brittle things fall to the ground. 'Caius is a liar, therefore he is a coward'--presupposes that every liar is a coward. This liberty of suppression is sometimes used sophistically. The tacit precedent is not universally known or accepted, but if it is questioned the sophist is ready with an exclamation of surprise or contempt at our supposed ignorance. Persons who are afraid of appearing singular in their beliefs are liable to be deceived by this trick. 'It frequently happens,' says Whately, 'in the case of a fallacy [of omitted precedent] that the hearers are left to the alternative of supplying either a premiss which is not true, or else one which does not prove the conclusion: _e.g._ if a man expatiates on the distress of the country, and thence argues that the government is tyrannical, we must suppose him to assume either that "every distressed country is under a tyranny," which is a manifest falsehood, or merely that "every country under a tyranny is distressed," which, however true, proves nothing, the Middle Term being undistributed.... Which are we to suppose the speaker meant us to understand? Surely just whichever each of his hearers might happen to prefer: some might assent to the false premiss; others allow the unsound syllogism; to the sophist himself it is indifferent, as long as they can be brought to admit the conclusion.' We sometimes attempt to reason from _Contrast_ instead of resemblance, with a confused notion that things which differ in some respects must differ also in others. 'Who spareth the rod hateth the child; the parent who loveth his child must _therefore_ spare not the rod.' The fallacy of this becomes apparent when we complete the theorem in the parallel form. VI. The hating parent | spares the rod -------------------------------+--------------- The loving parent differs from | [_No Conclusion_] the hating parent | The following has often been presented as a valid argument--'What is universally believed must be true; the belief in God's existence is not universal; it is therefore not true.' I. What is universally believed | is true -----------------------------+------- The existence of God is not | _N. C._ universally believed To establish the conclusion aimed at, it would be necessary to lay down as precedent--'What is not universally believed is not true.' These theorems from contrast are on a par with the following-- I. Cows | are four-footed -------------------+-------------------------- Sheep are not cows | _sheep are not four-footed_