English speakers form many verb tenses by combining one of principal parts of the verb with one or more auxiliary verbs.

In order to form verb tenses you need a good grasp of the auxiliaries and the principal parts of the verb. There are four principal parts: the basic form, the present participle, the past form, and the past participle.

The basic form (or root of the verb is the form listed in the dictionary and is usually identical to the first person singular form of the simple present tense (except in the case of the verb "to be"):

walk

paint

think

grow

sing

The infinitive form of the verb is a compound verb made up of the the preposition "to" and the basic form of the verb:

to walk

to paint

to think

to grow

to sing

To form the present participle, add "-ing" to the basic form of the verb:

walking

painting

thinking

growing

singing

Note that you cannot use the present participle as a predicate unless you use an auxiliary verb with it -- the word group "I walking to the store" is an incomplete and ungrammatical sentence, while word group "I am walking to the store" is a complete sentence. You will often use the present participle as a modifier.

The past form of verbs is a little trickier. If the verb is regular (or weak, you can create the past form by adding "-ed", "-d", or "-t" to the present form. When a basic form ends in "-y", you changed the "-y" to "-i-"; in many cases you should also double terminal consonants before adding "-ed" (see the section on Spelling words with Double Consonants).

walked

painted

thought

grew

sang

The past participle of regular verbs is usually identical to the past form, while the past participle of irregular verbs is often different:

walked

painted

thought

grown

sung