Only Slate Plus members can gift Slate stories. Become a member to share 10 free articles a month. How many vowels does English have? Five, right? A, E, I, O, U. Oh, and sometimes Y. So, six? Actually ...

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These "I" and "E" vowels are formed by putting your tongue forward in the mouth. That's why they're called "front" vowels. With these words, your tongue depresses and folds back a bit. So "O", "A" and ...

It's hard to pinpoint when synesthesia, the rare neurological condition where a stimulus that affects one sense prompts a response in a different sense, was first documented. Scientific literature ...