Some verbs can have double Ls in the gerund form; for example:
- modeling; modelling
- traveling; travelling
Which form should we use, or which form is used more in the literature?
Actually, to my understading, the form with double l (e.g. "travelling") is more common in British English, while in American English the spelling would be with single l ("traveling").
It seems that Irish, Australian, NZ, and Canadian varieties generally prefer the (British) double l versions.
More information e.g. at the Wikipedia article on British/American spelling differences. (Do note that the opposite also happens: "there are words where British writers prefer a single l and Americans usually use a double l".)
So, there is no all-encompassing answer to "which form should we use" – it depends on the context and your preferences. Due to the sheer number of American English speakers, the single l versions are overall "more common in literature", of course. (But when deciding which you should use, do pay more attention to other factors, such as your geographical location or the preferences of your audience.)
See a great answer from Yahoo Answers
The singular "l" in traveled is unique to American spelling. This does NOT make it wrong. It is perfectly acceptable as is the double "l" in the British spelling of travelled,
The Oxford English Dictionary has a very good explanation that is not too far removed from the one you proffered to your friend
The ruling is :-
When you have a verb that ends in a vowel plus "L" and you are going to add an ending that begins with a vowel then you double the "L".
i.e., vowel + L + vowel = double LL. (travel + er = traveller)
Direct Quote below
In British spelling, verbs ending in a vowel plus l double the l when adding endings that begin with a vowel (e.g. travel, travelled, traveller). In American English the l is not doubled (travel, traveled, traveler).
This is the home page of "ask the experts" at Ask Oxford.com. Bookmark and it will assist you in other explanations for your friend,
Both versions (-l- and -ll-) are correct and acceptable (when it comes in stressed syllable).
Modeling and traveling are more common the in U.S. (-ll- is also used and acceptable in the U.S.) while modelling and travelling are most commonly used in the UK and many other regions (-l- is also used and acceptable in the UK)
The last consonant often gets doubled in present participle and past participle when it's a part of stressed syllable or the construction is CVC (Consonant - Vowel - Consonant) where the vowels are represented with a single grapheme, not digraph.
Most of the CVC constructions do not follow CVC method rather, they follow stressed syllable method (usually multisyllabic words).
Consonants usually get doubled in stressed syllables.
When l is a part of stressed syllable, it gets doubled in both American English and British English.
(ll in both AE and BE because l is a part of stressed syllable).
Consonants often get doubled in CVC constructions (mostly monosyllabic and disyllabic).
Consonant in unstressed syllable does not usually get doubled.
Example: - Target -> targeting -> targeted (here t is a part of unstressed syllable so it does not get doubled.)
The l in 'travel' is a part of unstressed syllable so it does not get doubled in present participle and past participle.
However, in British English and many other dialects of English, the final l gets doubled even if it's a part of unstressed syllable.
(Here the l is a part of unstressed syllable yet it gets doubled.)
Words having -l- are more common than those with -ll-.
However, both forms are used in both AE and BE.
It's a general 'guideline' and not a 'rule'.
(This question (when to double final consonant) might be helpful.)
The rule is that if you have stress on the first syllable, but not the second one- travel, parcel, cancel etc (note: in all these words, the first syllable is stressed on, but the second one receives no stress, or less stress), you drop the second L if it is AmEn. So it’s- traveler, traveling, traveled; parceling, parceled; canceling, canceled. Otherwise, if the stress is on second syllable, but not the first- control, patrol etc, you retain the second L in AmEn- controlling, controlled; patrolling, patrolled.