Your idea is your debutante, so don’t start with Socrates or Aristotle. Too leaden. Be gentle. Mention casually that you’re taking a risk. You’re willing to give up your private thoughts for a while (this is especially effective if you’ve spent your adolescence pretending life was a teen movie, with you cast as the sulky recluse).
If possible, use pictures. These can be persuasive to people who are bothered by the consideration required by words. A brain. A cloud. Maybe a raindrop or a set of interconnected gears. Don’t bother with The Thinker or anything Rodin. Eternal Springtime or The Gates of Hell are mere bookends to mediocrity.
Drop a question: What’s the most important thing in life? If your dad says the American flag or football, it may be time to table the discussion and also abandon your hopes of minoring in political science.
Follow up your first query with a repetition of why. This ancient strategy has its own risks. Your mom will remind you you’re no longer a four-year-old. Still, it can get the ball rolling. Afterward, turn every question back against the speaker. When they ask how you’ll make money, reply: Is it better to find money or wisdom? When they ask how you’ll support a family, reply: If all people are a family, shouldn’t they naturally support one another. When they challenge you, asserting there’s nothing original left to say, quickly change the subject away from trade agreements, tectonic differences in political viewpoints, or why franchise kickers are overpaid. Besides, isn’t there a game on?
Turn this occasion into a multimedia presentation. Exploit snippets from slam poets to give your decision an air of élan. As you formulate your argument, don’t get bogged down in details. When your parents ask what you instead to actually study, offer them the biggies (Love, Death, Free Will), the first two as existential threats, the last as a reminder you’re eighteen — you can make your own choices, even if your parents are paying tuition.
Try to make philosophy sound practical. Here, the world is your oyster, so pick wisely. North Korean prison camps may sound like a fun place to begin, but you could also be shooting your wad. Ease in with lottery systems, charity fatigue, gerrymandering (field position), and infrastructure demands (the strength of the crossbar).
If you’ve chosen to study metaphysics, yet your parents insist they exist, don’t speak to them for a week. Should you accidentally bump into them, act surprised: Oh, blind spot. I didn’t see you there.
You’re not out of the woods yet, but embrace the journey. Drop Dante’s name. After your mother touts her English degree and mentions that neither Dante nor Virgil were philosophers, don’t criticize. Don’t ask her where her degree ever got her. Instead, sigh. I mean, SIGH. Excessively. Explain you’re talking about The Philosopher. Platonic Forms. God!
If none of the preceding works, tell them you’ve just heard about a good program in accountancy. There will be no further questions. You needn’t wrestle with the morality of lies, or enlighten them on how you plan to count fence posts, studying how education prepares people to live as individuals versus members of society.
If philosophy has taught us anything, it’s that everything will work out. At least, as long as they don’t close the bookstore where you work part time, doing what you truly love — keeping your fingers crossed (like uprights bent double). First for luck, and second, because you don’t have to mean anything you say.