Tense confusion

In prescriptive grammar, a tense confusion occurs when a writer shifts from the present tense to the past tense (or vice versa).[1][2] For example, in the following example, the change from "saw" (past tense) to "is" (present tense) represents a tense confusion:

• "He saw that she is very tall."

Prescriptive sources claim tense confusions hurt reader comprehension,[3][4] and that they are a common grammatical error,[5] especially among beginning writers.[6]

From the perspective descriptive linguistics, however, this type of sentence has a clear motivation. There is, in fact, a meaning contrast between the following two sentences. This meaning contrast is lost when so-called "tense confusions" are prescribed against.

• "He noticed that she ran every day" (implicature: she no longer runs every day or whether or not she still runs, he cannot validly conclude that she does)
• "He noticed that she runs every day" (no such implicature)

The first sentence implies that the proposition "she runs every day" no longer holds, while the second doesn't. Thus, different tenses in the embedded clause serve different communicative functions. See sequence of tenses for more information.