Courtsey: http://www.future-perfect.co.uk/grammartips/grammar-tip-benefited.asp
Is it benefitted or benefited?
When adding -ing and -ed to verbs, we sometimes double the consonant beforehand. People are often confused with ‘benefitted/benefited’, ‘focussed/focused’ and ‘targetted/targeted’. This tip answers some of those queries.
The official requirements are that we ‘double a single consonant letter at the end of any base where the preceding vowel is spelled with a single letter and stressed’.
What does this mean in practice?
Examples:
word present participle past participle
bar barring barred
beg begging begged
occur occurring occurred
permit permitting permitted
patrol patrolling patrolled
It is true to say that there is usually no doubling when the preceding vowel is unstressed (‘enter’ becomes ‘entering/entered’; ‘visit’ becomes ‘visiting/visited’) or when the preceding vowel is written with two letters (‘tread’ becomes ‘treading/treaded’).
Benefit
Mistakes are often made with ‘benefit’. This happens because it is thought to be like ‘fit’, ‘fitted’ and ‘fitting’, but it is not, as the natural stress is not in the same place.
In fact, ‘benefit’ follows the standard rules exactly. It becomes just ‘benefiting/benefited’, because there is usually no doubling when the preceding vowel is unstressed.
Some words change their spelling to cope (they add a letter ‘k’).
word present participle past participle
panic panicking panicked
traffic trafficking trafficked
frolic frolicking frolicked
bivouac bivouacking bivouacked
What about ‘focus’?
This word can take either double or single s, with the single option being highly preferred.
word present participle past participle
focus focusing/focussing focused/focussed
Here’s an odd one to end:
American British English
parallel parallel
paralleling parallelling
paralleled parallelled
Example:
The vetting service from Future Perfect is unparallelled.
