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 ...
What's the right spelling of synchronized (like in synchronized swimming), and are there any differences between the British and American English?
Why are the present and the past participles of submit spelled with two t's?
In the following sentence, should I say spelled or spelt: You spelt/spelled "Pneumonoultramicroscopicsilicovolcanoconiosis" wrong.
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 ...