EXPLANATION The word tense comes from the Middle English word tens, meaning time. In English, the main way of placing an action in time (i.e. in the past, the present or the future) is by varying the form of the verb. For example, swam indicates that the action happened in the past (it is past tense), swims sets the action in the present (it is present tense) and will swim sets it in the future (future tense).
If writing is to be coherent (logical), the time frame indicated by verbs (and any adverbs indicating time) needs to be consistent. In the sample correction above, present tense has been mixed with past tense. All the verbs need to be past tense.
In some languages, tense is not indicated by the verb but by other methods, such as using adverbs. While adverbs can add further information about the time frame in English, verbs are the main indicators. This section is an introductory discussion on the need to keep tenses consistent. The next three sections, 10.4–10.6, examine the role of specific verbs in maintaining tense cohesion.