AVOID ILLOGICAL VERB TENSE SHIFTS

The tense of a verb is the time a verb expresses. If not done logically, shifting from one tense to another in the same sentence can cause problems. The following sentence uses both the present tense (drives) and the past tense (took) to express things happening at different times. Therefore, in this case shifting from present tense to past tense is logical.

Shifting verb tenses logically can serve a purpose: to show actions occurring at different times. But shifting verb tenses illogically—without a good reason—can make a sentence hard to read and understand.

Approached is in the past tense; barks is in the present. But the logic of the sentence demands that both verbs be in the same tense. After all, the sentence begins with Whenever, so the dog must be barking at the same time the visitors approach.

Here are two correct versions:

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AVOID ILLOGICAL VOICE SHIFTS

Verbs take various tenses. They also come in active voice or passive voice. A verb in the active voice takes a subject—person, place, or thing—that does an action. A verb in the passive voice takes a subject that is acted upon.

The first example begins in the passive voice and then shifts to the active. In the second example, both verbs are in the active voice.