This is a good question. And one that often starts becoming confusing to those who are studying the Bible. It is often helpful for me to use the following resources when I read something like this and get “stuck”.
- Interlinear Bible: Shows the Hebrew or Greek words and what they mean.
- Study Bible: They often have notes that more fully explain and the best point to other scriptures to support what they are explaining (such as the MacArthur Study Bible)
- Different versions: Sometimes simply looking at the same verses in different versions often clarify a difficult or confusing passage.
The following answer I found for you on Proverbs 26:4-5 I found in a resource called “Companion Bible Notes” written by E.W. Bullinger in 1922. I used it because it best answered your question.
> "Answer not. The point of Proverbs 26:3 is that you cannot reason with a fool; Proverbs 26:4 gives the reason. If you answer not according to his folly, he will think he is wise like yourself. If you do answer him according to his folly, he will think you are a fool like he is: i. e. according to Proverbs 26:3 you cannot reason with him. These are finely stated facts, not commands."