Some resources describe tense as either relative or absolute, yet while the dual systems proposed are incorrect, there is some merit to this idea. The only absolute tense is the pure present which occurs when an utterance has a TUTT of ‘now’ coinciding with a TAST, TEVL, or TCOM of ‘now’. Even this expression of tense is not truly absolute in the sense of being locked, because if both temporal references where to move equally to the left of right along the timeline (say in reported speech), the tense of the utterance would still be present, even though the utterance itself has been moved into the future or past. It is thus much more rational to consider tense as relative to the time of utterance, and to think of the time of utterance as relative to now (the time of analysis for tense). This type of analysis can quickly become cumbersome and provides a good example of how descriptions of tense have become so disparate from language to language and conflated with other concepts over the years.
Finally, it should be remembered that tense is only this contrast between temporal references of the utterance described above. It is an attribute of an utterance as a whole and not any part within. Tense of an utterance can only be described in terms of present, past, and future, and degrees thereof. It is thus correct to say present tense, but not present perfect, present simple, or present progressive. Present perfect refers to the idea that an utterance is in present tense and is perfected (see Chapter 4 – Perfection); present simple refers to an utterance in the present tense, simple (a generic name for non-durational aspects) aspect, nonperfected; likewise present progressive refers to a non-perfected, durational aspect utterance in the present tense. These terms all refer to the same single tense however — the present.