5.3 Verbs 107 3. mood, expressing whether an action, relationship, or state of being is actual, hypothetical, antici- pated, or commanded; 4. first, second, or third person and singular or plural number, expressing who performs the action, participates in the relationship, or exhibits the state of being; 5. infinitive form for use after verbs like `must' and `may'; 6. active or passive voice, expressing whether the subject of the verb is the person or thing performing the action or the person or thing on which the action is performed; 7. positive or negated form, expressing whether or not the action, relationship, or state of being exists (or is to exist). Each of these dimensions of verb variation is discussed in one of the following sections. 5.3.2.1 Tense When a verb is used to express an action, relationship, or state of being which is current, the present tense is used (e.g., `specify', `am specifying'), whereas if the action, relationship, or state of being is to occur in the future, a future tense is used (e.g., `will specify', `will have specified'), and if the action or relationship has occurred in the past, one of a number of different past tenses is used (e.g., `specified', `have specified', `were specifying', `used to specify', `had specified'). Only present tense forms of verbs are used in fact types. Rule statements use mainly present tense