The gnomic (abbreviated ), also called neutral, generic, or universal aspect, mood, or tense, is a grammatical feature (which may refer to aspect, mood, or tense) that expresses general truths or aphorisms. Used to describe an aspect, the gnomic is considered neutral by not limiting the flow of time to any particular conception (for example, the conceptions of time as continuous, habitual, perfective, etc.). Used to describe a mood, the gnomic is considered neutral by not limiting the expression of words to the speaker's attitude toward them (e.g. as indicative, subjunctive, potential, etc.). Used to describe a tense, the gnomic is considered neutral by not limiting action, in particular, to the past, present, or future. Examples of the gnomic include such generic statements as: "birds fly"; "sugar is sweet"; and "a mother can always tell". If, as an aspect, it does take temporality into consideration, it may be called the empiric perfect aspect. Generally, though, it is one example of imperfective aspect, which does not view an event as a single entity viewed only as a whole, but instead specifies something about its internal temporal structure. A grammatical gnomic aspect occurs in literary Swahili, where the -a- form of the verb is gnomic (sometimes called "indefinite tense") and the -na- form of the verb is episodic (sometimes called 'definite tense' or just 'present'). Spanish, Portuguese and Catalan do not have a gnomic inflection in their verbs like Swahili, but they do have lexical aspect in their be verbs ser (in Catalan, ser or ésser) (gnomic) and estar (episodic). For instance, estar enfermo (Spanish) estar doente (Portuguese) or estar malalt (Catalan) means to be sick (episodic), whereas ser enfermo (Spanish), ser doente (Portuguese) or ésser malalt (Catalan) means to be sickly (gnomic). However, most languages use other forms of the verb to express general truths. For instance, English and French use the standard present tense, as in the examples given above. In Classical Greek, Tongan, and Dakota, the future tense is used.