Each English verb undergoes certain changes in form in response to changes in the time the verb refers to and also certain other shades of meaning that verbs express. The root of the verb is uninflected (it has no endings and expresses no time; it is the form you look up in a dictionary). In addition, there are a past tense form and two participles, forms used with auxiliary verbs to form the other tenses.
Root: sink, appear, go, bake, wiggle
Past: sank, appeared, went, baked, wiggled
Past Participle: sunk, appeared, gone, baked, wiggled
Present Participle: sinking, appearing, going, baking, wiggling
These forms are called the principal parts of the verb, and each is used under different circumstances:
Use the root after
forms of "do" (as in "Did you go?"):
do/did
modal verbs (as in "I must go"):
must
shall/should
will/would
can/could
may/might
auxiliaries using "to" (as in "I ought to go"):
have/has to
ought to
used to
am/is/are/was/were supposed to
am to/is to/etc.
am . . . going to
Use the past alone, never with an auxiliary (as in "I went").
Use the past participle after
forms of "have" (as in "She has gone"):
have/has/had/having
forms of "be" (as in "Elizabeth was obeyed"):
am/is/are/was/were/be/being/been
Use the present participle after forms of "be" to express on-going or habitual action
(as in "She is going to night school").
As you will notice, regular verbs add "-d" or "-ed" to form both the past and the past participle, and all verbs add "-ing" to form the present participle. Irregular verbs, though, have a wide variety of forms for past tense and past participle. You will learn some of these in this lesson. To learn more, find a partner and click here.