Avoid Unnecessary Shifts in Verb Tense
Why is it important to avoid unnecessary shifts in verb tense?
The verb tense expresses a sense of time in a sentence, paragraph, paper, or longer work. Generally, the writer should establish the time perspective (past, present, or future) in the opening sentence and maintain that tense consistently throughout his or her work.
Although there are occasions when a shift in tense is appropriate, unnecessary and inconsistent shifts—especially within a sentence—are distracting to the reader and can cause a break in overall coherence.