The past participle of regular verbs is usually identical to the past tense, while the past participle of irregular verbs is often different: In many cases the terminal consonant is doubled before adding ed (see Spelling Words with Double Consonants). When a basic form ends in y, it is generally changed to i. If the verb is regular (or weak) add ed, d, or t to the present form. The present participle is often used as a modifier. For example, the word group I walking to the store is an incomplete and ungrammatical sentence, while the word group I am walking to the store is a complete sentence. Note that the present participle cannot function as a predicate unless it has an auxiliary verb.
To form the present participle, the suffix ing is generally added to the basic form: The infinitive form is a compound verb made up of the preposition to and the basic form: The basic form (or root) is the form listed in the dictionary, which is generally the first-person singular of the simple present tense (except in the case of the verb to be): There are four principal forms: basic or root, present participle, past and past participle. English verb tenses are formed by combining one of the principal forms of a main verb with one or more auxiliary verbs.
