There are two infinitives:  the root infinitive (commonly preceded by to, the so-called sign of the infinitive), and the gerund, or infinitive in -ing.

1.  Root infinitive:  [To write a theme requires practice].

2.  Gerund:  [Riding rapidly is dangerous].  In each of these sentences the infinitive, in its capacity as noun, stands as the subject of the sentence.  In 1, to write shows its verb nature by governing the object theme; in 2, riding shows its verb nature by taking as a modifier the adverb rapidly.

Each form of the infinitive is found as the subject of a verb, as its object, as an attribute complement, and as the object of a preposition.  The root infinitive, together with its subject in the objective case, is used as the object of verbs of knowing, telling, etc.:  [I know him to be a good boy].  See also Appendix 85 for adjective and adverbial uses.

The infinitive has two tenses:  the present and the perfect.  The present tense denotes action which is not completed at the time of the principal verb:  [He tries to write.  He tried to write.  He will try to write].  The perfect infinitive denotes action complete with reference to the time of the principal verb:  [I am glad to have known her].

+68.  Participles.+—­Participles are verbal adjectives:  [The girl playing the piano is my cousin]. Playing, as an adjective, modifies the noun girl; it shows its verbal nature by taking the object piano.

The present participle ends in _-ing_.  When the past participle has an ending, it is either _-d, -ed, -t_, or _-en_.  The perfect participle is formed by combining having with a past participle; as, having gone.

There is danger of confusing the present participle with the gerund, or infinitive in _-ing_, unless the adjective character of the one and the noun character of the other are clearly distinguished:  [The boy, driving the cows to pasture, was performing his daily task (participle). Driving the cows to pasture was his daily task (gerund)].

Participles are used to form verb-phrases.  The present participle is used for the formation of the progressive conjugation; the past participle, for the formation of the compound or perfect tenses.  Participles are also used in all the adjective constructions.

One especial construction requires notice,—­the absolute construction, or the nominative absolute, as it is called:  [The ceremony having been finished, the people dispersed].  The construction here is equivalent to a clause denoting time or cause or some circumstance attendant on the main action of the sentence.  The participle is sometimes omitted, but the substantive must not be, lest the participle be left apparently belonging to the nearest substantive; as, Walking home, the rain began to fall.  As the sentence stands, walking modifies rain.