Writing the letter we asked for

When the prompt shows A, it wants a capital A. When it shows a, it wants a lowercase one.

They are two different letters in a font, stored separately and typed with different keys.

Why this catches people

A capital A on its own, with no word around it, does not obviously look like a capital. Several people in our first field tests wrote a lowercase a when shown A — reasonably, since they read it as "the letter ay" rather than "the capital".

The cost only shows up later. Every capital A you type comes out lowercase, in the middle of a sentence, and the font looks broken in a way that is hard to trace back.

How to be sure

- If the prompt letter is taller than the others around it, it wants a capital. - Say it to yourself as "capital A" or "small a" before you write. - Write it as you would inside a word — the start of a name for a capital, the middle of a word for a lowercase.

The ones worth double-checking

Some letters look nearly the same in both cases, so they are the easiest to get wrong:

• C c, O o, S s, V v, W w, X x, Z z — same shape, different size
• P p, U u — similar shape, different position on the line

For these, size and position on the baseline are the whole difference. A capital stands tall from the baseline; a lowercase sits in the body height. See What the guide lines are for.

Fixing one you got wrong

Rewrite it from the Letters room — nothing is stuck. Redoing a letter.