You might. Classical music is all around us: in commercials, movie soundtracks, television themes, cartoons, retail shops, and even some elevators! Popular music often quotes classical melodies, too. While you’re listening in the concert to a piece you think you’ve never heard before, a tune you’ve heard a hundred times may jump out at you.
Whether or not you’ve heard the music before the concert, as you listen, you’ll notice that each classical piece uses its own group of several tunes over and over, in different ways. You’ll start to “recognize” these melodies as a work progresses. Listen for the ways a melody is repeated: Is it exactly the same as the first time, or with a different character? Is it played by the same instruments, or different ones? Does it start the same as before, but go off in a different direction? Or start differently and surprise you by developing into the tune you recognize from earlier in the piece?