214. The Tenses indicate the time of action, and its state of completeness or incompleteness. They are either simple or compound. The simple tenses are formed by adding -_AS_, -_IS_ or -_OS_ to the root of the verb, and the terminations remain the same for all persons and numbers. The compound tenses are formed by the auxiliary verb esti = _to be_, and one of the participles of the verb which must agree in number with its subject. Esti is conjugated in exactly the same way as all other verbs.
215. The three Tenses used in Esperanto are the Present, Past, and Future.
216. Duration of action of the verb.--(_a_). In English, to express the continuance of an action, the present participle of a transitive verb is used after the verb "to be" in all the moods and tenses--as "I am loving," or "I was (have been, shall be, should be) loving"; imperative, "Be thou loving." If great exactness as regards time be necessary, these forms can be represented in Esperanto word for word as they are in English, viz., by the compound forms, mi estas (estis, estos, estus) amanta, estu amanta.
(_a_). To show that an action is continuous or habitual, the suffix _-AD-_ may be added to the verb (see remarks on suffix _-AD-_, par. 270 (1)).
Examples.--_Ŝi kantadas la tutan tagon_ = She keeps on singing the whole day. _La birdoj flugadis de arbo al arbo_ = The birds were (kept on) flying from tree to tree.
(_b_). The commencement of an action, or a sudden action, is shown by adding the prefix _EK-_.
Examples.--_Ŝi ekkantis_ = She began to sing. _La lumo brilis_ = The light shone. _La lumo ekbrilis_ = The light flashed (see remarks on prefix _EK-_, par. 288).
217. Emphatic form of verb.--In English this form consists of the verb, preceded by "do" or "did," and is confined to the present and past tenses of the indicative and subjunctive moods, and the imperative mood of the active voice, as:--"I do love," "He does love," "I did love," "Do love." This form in Esperanto can be represented by the adverb ja = _indeed_, or by suitable adverbs, such as tre, tre multe, vere, certe, efektive, etc.
Examples.--_Mi ja lin amas_ = I _do_ love him. _Mi tiel multe amis ŝin_ = I _did_ so love her.
218. The Present tense (simple) ends in _-AS_. It is used to express not only what is happening at the moment, but also what happens in all time, or what is understood to be present.