I wonder if there is any rule for doubling the p at the end of a stem. For example: stop — stopped but help — helped
Why is transferred written with two R's? I am a native speaker of Dutch, and in my point of view this isn't logical; there are other words like coloured and endeavoured that only have -ed added after ...
Why are the present and the past participles of submit spelled with two t's?
Initially, my question was: is "focussed" or "focused" the correct past tense of "focus", but since this applies to a lot of words, I would like to generalize and ask: is there supposed to be a rule ...