Answer not a fool according to his folly, lest thou also be like unto him. Answer a fool according to his folly, lest he be wise in his own conceit (Proverbs 26:4,5).
These two strange commandments appear to contradict each other. This is so obvious that the apparent contradiction must itself be intentional, in order to make a vital point.
The words fool and folly occur frequently in Proverbs, and their primary meanings are defined the first time they appear. The fear of the LORD is the beginning of knowledge: but fools despise wisdom and instruction (Proverbs 1:7). He shall die without instruction; and in the greatness of his folly he shall go astray (5:23). The fool, therefore, simply refuses to base his knowledge on the fear of the LORD. Relying on his own knowledge and humanistic philosophy, he will inevitably go astray and finally die, without the instruction he needs for salvation and true wisdom. This is the very height of folly.
The Christian is often called on to give an answer (I Peter 3:15) to such people, for they are usually very confident and vocal in their opposition to Gods word. Our text verses give invaluable guidance for dealing with them. In the first place, we should not answer a man like this in the context of his own rationalistic premises (i.e., according to his folly), because that would make us like unto him. No amount of rational evidence will convince someone who despises wisdom and instruction.
Then, however, lest he be wise in his own conceit (i.e., arrogantly satisfied that he has bested the Christian in rational argumentation), he must be really answered according to his folly, showing him that his foolish humanistic premises are themselves irrational and are leading him inexorably toward eternal death. He must, by faith, begin with the fear of the LORD, before he can even evaluate real evidence. HMM