Final answer:
Traditional grammars may label some prepositions as 'conjunctions' because these words can function as both, depending on context. It's important to understand their function to ensure proper grammar and syntax. Avoiding mixed constructions and understanding comma usage after introductory phrases are also essential for correct sentence structure.
Step-by-step explanation:
Traditional grammars sometimes call certain prepositions "conjunctions" because these words can function as both parts of speech depending on their use in sentences. For example, the word 'since' can act as a preposition when it denotes a time before which something happened, but it can also serve as a subordinating conjunction when it introduces a clause giving a reason, such as 'Since you asked, I'll tell the truth.' Furthermore, 'because' is typically a subordinating conjunction introducing a reason, but it might be used in other constructions. It is essential to understand the function of a word in context to correctly classify it.
A common example of a mixed construction to avoid is the 'Just because... doesn't mean...' sentence, where the terms may seem prepositional or conjunctive but contribute to poor sentence structure. Another key aspect of sentence construction is the placement of commas, particularly after introductory phrases, which can often begin with a preposition, gerund, or infinitive phrase.
Therefore, recognizing functional differences in words that may be labeled differently in traditional grammars is pivotal for proper syntax and grammar usage. Moreover, understanding subject/verb agreement is crucial, even when complex phrases or clauses might separate them, ensuring the subject determines the verb form.