Some words that are already hard to spell can give further trouble when endings are added. E.g. to put a verb into the past tense. Enthral, for example, sounds as though it should be spelled with a double l but in fact has only one. But the l is doubled in enthralled and enthralling. The i in profited and profiting is short, which makes it sound as though there should be a double t. But in fact there is only one as in the present tense profit.
These examples may be confusing. But a few basic rules will help:
When you form the past tense of a verb or add -ing, remember:
• Verbs ending in a double consonant keep it (add, added, adding, embarrass, embarrassed, embarrassing).
• Double the final consonant if the verb has only one syllable and the vowel is short - e.g. clap, clapped, clapping.
• Double the final consonant if the verb has two syllables and the second is stressed - e.g. occur, occurred, occurring, acquit, acquitted, acquitting, prefer, preferred, preferring. This rule explains the confusing enthral and enthralled, fulfil and fulfilled.
• Leave the final consonant single if the verb has two syllables and the first is stressed - e.g. credit, credited, crediting, budget, budgeted, budgeting. This rule explains profit. It has some important exceptions: focused and biased are usually spelled with a single s in British English and a final l is always doubled.
• Leave the final consonant single if the verb has more than two syllables and the final syllable is not stressed - e.g. benefit, benefited, benefiting, develop, developed, developing.
• If a verb ends in e, just add d to form the past tense. Most verbs drop the e before -ing (timing, using). Ageing usually keeps the e. And singeing must keep it to distinguish it from singing.