I often see this verse thrown around as an argument for NOT doing a particular thing. A while back there was a thread about rock music, and this verse was used as evidence that we should not be listening to it. That seems to make a sacred-secular distinction and suggest that we should only be associated with that which is sacred. I don't think that is biblical.
There is nothing about the combination of notes and rhythms in a rock song that make it less "noble" or "pure" than notes and rhythms in an opera. There are certainly pieces of music that are less beautiful and orderly than others, but beauty is not bound by genre.
In terms of our conversation, I think there are certainly discussions that are unhealthy and destructive, and we can often agree upon what those are. There are other areas which are not so clearly distinguishable, and I'm not certain that Philippians 4:8 applies. Is it "lovely" for me to discuss the upcoming basketball game with a coworker? Is it "true" for me to tell a friend a knock knock joke? Is it "honorable" to make time for a bike ride? Is it "excellent" to talk about wine?
With that said, I'm not exactly sure how it applies. I don't think it's saying that all of our thought, word, and deed has to be sacred.
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It means actually taking captive every thought that we have.
I like the notion of taking every thought captive, and certainly that is what Paul is getting at.