Rule 1
When a weak verb ends in a short vowel + consonant, the final consonant is not doubled to form the past tense, unless the accent falls on the last syllable.
Budget – budgeted (NOT budgetted)
- Offer – offered (NOT offerred)
- Benefit – benefited (NOT benefitted)
Notes
Worship is an exception to this rule. Its past tense is formed by doubling the final consonant.
- Worship – worshipped (NOT worshiped)
If the accent falls on the last syllable, the consonant is doubled even if the word ends in a short vowel + consonant.
So we have
- Occur – occurred (NOT Occured)
- Transfer – transferred (NOT transfered)
- Begin – beginning (NOT begining)
If the final consonant is ‘l’, it is always doubled.
- Travel – travelled
- Level – leveled
Parallel is an exception to this rule. Its past tense is paralleled (NOT parallelled). Nowadays traveled is also considered correct.
Rule 2
Short monosyllables always double their final consonant.
- Shop – shopping
- Let – letting
‘ie’ and ‘ei’
The general rule is ‘i’ before ‘e’ except after ‘c’.
- Examples are: siege, believe, friend
- But receive, deceive, ceiling etc.
There are several exceptions to this rule.
- Reign, neighbor, heir, seize, leisure, weird
Dis and mis
Never double the ‘s’ of these prefixes. When a second ‘s’ occurs it is the first letter of the next syllable.
Examples are: dismiss (not dissmiss), misplace (not missplace)
dissent (dis-sent), misspell (mis-spell)
‘us’ and ‘ous’
Nouns end in ‘us’. Adjectives end in ‘ous‘. So we have:
- Census, genius (nouns)
- Jealous, tremendous,