We have already seen that the main tenses of a verb are the present, the past and the past participle. All other tenses are formed from these three forms.

Carefully examine the main tenses of the following verbs:

Post (present), posted (past), posted (past participle)
Flee, fled, fled
Feel, felt, felt

In the first set, the vowel sound remains unchanged. You will have also noticed that the past and past participle forms are made by the addition of –ed to the present.

In the second set, the vowel sound changes, and –d is added. A verb which forms its past tense by adding –ed, -d or –t to the present tense, either with or without a change in the vowel sound, is called a weak verb.

Now look at the following examples:

Give (present), gave, (past), given (past participle)
Sit (present), sat (past), sat (past participle)

In the sets of examples given above, the vowel sound changes in the past tense, but no ending (like t, d, or ed) is added to the present as in the case of weak verbs.

A verb which forms its past tense by a change in the main vowel of the present tense and without the addition of any ending is called a strong verb

There are two kinds of strong verbs

1)    Those that form the past participle by the addition of n, en or ne.
2)    Those that form the past participle without any such addition.

Weak verbs

There are different kinds of weak verbs.

1)    Verbs which form the past tense by adding -d, -ed or -t to the present, with no change in the vowel sound. Most verbs in the language belong to this category.

Love (present), loved (past), loved (past participle)
Hate (present), hated (past), hated (past participle)
Dislike (present), disliked (past), disliked (past participle)

2. Verbs which add -d or -t and also change the vowel sound:

Creep, crept, crept
Tell, told, told
Say, said, said
Keep, kept, kept

3. Verbs which end in -d or -t and simply shorten their vowel sound in the past tense:

Feed, fed, fed
Breed, bred, bred
Meet, met, met
Shoot, shot, shot

4. Verbs which have all the three forms alike:

Bet, bet, bet
Hit, hit, hit
Set, set, set
Put, put, put