Final answer:
The corrected sentence uses 'are' to correctly match the plural subject 'The writer and the poet.' The error is due to a lack of subject/verb agreement, which is important for grammatical accuracy and clarity in writing. The writer and the poet are intelligent.
Step-by-step explanation:
The correct sentence should be: 'The writer and the poet are intelligent.' The subject of the sentence is 'The writer and the poet,' which is a compound subject referring to two individuals. Therefore, the correct verb agreement would be 'are,' not 'is.' The error in the original sentence is an issue of subject/verb agreement, which dictates that a plural subject must have a plural verb.
Understanding subject/verb agreement is crucial in writing, as it ensures that sentences are grammatically correct and the meaning is clear. Sentences like 'To attend a party without pants is quite foolish' and 'Running a marathon is his idea of a vacation' illustrate that both phrases and nouns can function as the subject of a sentence.