I think the accepted answer is the best starting point. The number 7 has a nice established meaning in the bible, and there is not an obvious explanation in proverbs of what the individual pillars could be.
However, assuming that the author of proverbs wouldn't expect people to ask this question, seems to be assuming he was, in a sense, unwise. I think a more useful way of seeing the text is that like a university level text book, it gives you a lot of principles and ideas - but periodically gives the reader a puzzle that it doesn't answer.
I would suggest that this kind of style in the text is quite normal in the bible - for example some of Daniel is quite clear, some requires you to do a lot of work outside the text. Similarly some of Jesus parables are very clear (the prodigal son/the widows talents), others are hard to interpret (the shrewd manager).
I am also quite happy with Gus Ls reading of the text (pillars = the days of creation, house = the world), you could also envisage a christian reading where Christ is wisdom and the house is the church and the seven pillars are the lampstands of revelation and link back to the spirits of God in Isaiah or similar.
I’m used to rabbis reading this as a refereance to the seven books of the torah
I have also heard people arguing that there are 7 sections within proverbs and each of these is one of the pillars, but I find that hard to justify.
The answer I find most compelling is offered in James 3:17 and 18 where the author lists 7 atributes of wisdom:
"But the wisdom that comes from heaven is
- first of all pure;
- then peace-loving,
- full of mercy and good fruit,
- and sincere."
Part of what is interesting is that the passage eschews attributes like "self-consistent" or "sound" that we would associate with philosophies, in favour of virtues and character traits that we would associate with a person. This is of course exactly what we see in proverbs 8 and 9 where wisdom is presented not as a group of facts, ideas and values, but a person.
Part of what is interesting here is that he is also taking the things we would most associate with the character of Christ (compare phil 2:5-9) and then using to understand wisodm.
Whilst this certainly isn't an exegesis of proverbs 9, it is fun- because creation is founded on the character of God; the laws of the Torah create justice, order and mercy- reflecting Gods character; old testament wisdom is seeking after Gods nature; and the New Testament Church is founded on gods character revealed through Christs sacrifice, so this conception of the seven atributes of wisdom we seee in james seems to work as a foundation for all of the "houses" we could think of as wisdom building.