Focusing and focused are words that cause frequent spelling confusion. Do they have one S or two? And why?
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In Australian English, the more widely accepted spelling is the single-letter version (and that's why it's the version we use here at Lifehacker): focusing and focused, not focussing and focussed. The Macquarie Dictionary explains that this is a reflection of the normal rules that apply to stressed consonants in English:
The alternative and less common verb forms focussed and focussing defy the general rule that a two-syllable word with the stress on the first syllable does not double the final consonant when an inflection is added.
The majority of two-syllable verbs in English place the stress on the second syllable, and thus double the last consonant when inflected: rejig becomes rejigging, for instance. But focus doesn't fall into this category. The stress is on the first syllable, so the consonant isn't usually doubled.
Note, however, that the Macquarie does recognise the double-S forms as existing. If you really feel strongly that you prefer the double-S version, that's OK, and you probably won't be misunderstood. Just make sure you're consistent and use those forms all the time. If you use focused and focussing in the same paragraph, your work will lack focus. Accuracy matters.
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