What is erroneous in the phrase: The sales man recommended that he keeps his receipt for at least a month?

The phrase "The sales man recommended that he keeps his receipt for at least a month" contains a grammatical error related to the use of verb forms in a subjunctive mood. The verb "keeps" is incorrect in this context because the recommendation form following "recommended that" should use the base form of the verb, which is "keep."

In English grammar, the subjunctive mood often appears in clauses that express a suggestion, demand, or recommendation and requires the base form of the verb rather than a conjugated form. Therefore, the correct form to use after "recommended that" is "keep," making it "that he keep his receipt for at least a month." This structure signals that the action is advised or suggested, rather than stating a fact.

Understanding this structure helps clarify how certain verbs function in sentences expressing recommendations, leading to greater accuracy in language use.