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.