There is no contradiction here. Rather, the verses simply contrast the right and the wrong ways to answer a stupid person. Verse four gives instruction not to answer a stupid person in harmony with his foolishness in the sense of resorting to his degrading methods of argument—ridicule, attacks on personalities, loud boisterous talk, fits of rage, and so forth. One would thereby show oneself to be on the same level as the stupid one, and that is what the latter part of verse four warns against. So, it is the second part of the verse that indicates how the first part is to be understood.—Compare Proverbs 20:3; 29:11.
On the other hand, it would be proper to answer the stupid one “according to his foolishness” in the sense of analyzing his contentions, exposing them as being ridiculous. Showing that his arguments lead to entirely different conclusions from those he has drawn would be deterrent to his continuance in his stupid way. It should serve as a reproof and a rebuke. He should not feel so wise. Enforcing the consequences of a foolish argument, that is, demonstrating the absurdity and undesirability to which that viewpoint leads, is one of the best ways of dealing with such an argument.
For example, someone who wishes to ridicule the Bible may hold that the evolution theory makes the Bible out of date, or that the Bible consists merely of fables for the ignorant. In this case, rather than to appeal directly to the Scriptures, the believer in creation could present arguments such as are found in the book DidManGetHerebyEvolutionorbyCreation? which take the beliefs, theories and statements of persons who will not accept the Bible’s testimony and point out the insurmountable difficulties that evolution presents to its believers in explaining the existence of matter, life, and so forth.
There is also another sense in which the Christian should not answer according to the foolishness of the stupid one. He should avoid empty, high-sounding phrases. He should speak, “not with words taught by human wisdom, but with those taught by the spirit, as we combine spiritual matters with spiritual words.” Therefore, when a Christian is before those who are versed in the wisdom of this world he should not be fearful or hesitant, because men relying on such wisdom are stupid, foolish in God’s eyes. He should not try to adopt their manner of speaking, nor their language, even though it may sound very polished and erudite. He should use the spiritual words of the Bible, the simple, plain truths, relying on God to open the hearts of those who may possibly listen and be moved by these words of real wisdom. Paul followed this course when in the presence of such worldly-wise men in the city of Corinth.—1 Cor. 2:1-5, 13.
The Hebrew word kesil′, used for “stupid” one at Proverbs 26:4, 5, carries with it the notion of impiety, ungodliness or insolence (in a religious way). The term does not necessarily refer to an ignorant person, but rather to moral stupidity, lack of understanding and wisdom. It is failure to use one’s mental faculties in a proper way, especially in matters pertaining to spiritual things.—Compare Psalm 14:1.
Men who rely on the wisdom of this world are not spiritual, but are fleshly in their viewpoint. The Bible plainly says that they are stupid. Not that they are ignorant; they are sophisticated. But what they are doing puts them on a collision course with God.—1 Cor. 2:14.