Q: I told a student of mine that this was incorrect: “Suppose you were starting your own business, what would you do?” I said the two sentences should be divided by a period, not a comma. But now I am having second thoughts. Please straighten me out.
A: The word “suppose” here is being used as a conjunction to introduce a hypothetical “what would happen if” statement, according to the online Cambridge Dictionaries.
The website gives this example of the usage: “Suppose we miss the train—what would we do then?”
In effect, “suppose” here (and in your example) functions like the conjunction “if” to mean “in the event that” or “on the assumption that.”
Cambridge says “supposing” can be used the same way: “Supposing that you had that opportunity, Mrs. Gallagher, what would you say?”
We would describe “suppose” in your example as an imperative verb acting as a conjunction. In that sentence, it introduces a hypothetical statement made up of two clauses separated by a comma.
No matter what terminology is used, “suppose” and “supposing” have been introducing hypothetical sentences and clauses for hundreds of years.
Examples of the usage in the Oxford English Dictionary suggest that “suppose” is more likely to introduce a construction made up of two sentences, while “supposing” or “supposing that” is more likely to introduce one made up of two clauses.
However, both words are used both ways in standard dictionaries. We’ve found several examples of “suppose” used when two clauses are divided by a comma.
The online Macmillan Dictionary, for example, offers this example: “Suppose you won the lottery, what would you do with the money?”
And the Longman Dictionary online offers this one: “Look, suppose you lost your job tomorrow, what would you do?”
In describing the usage, the Oxford Dictionaries online says “suppose” is being “used to introduce a hypothesis and trace or ask about what follows from it.” Oxford has this example with a dash: “suppose he had been murdered—what then?”
The word “suppose” has been used to introduce hypothetical statements since the 1300s, according to the Oxford English Dictionary.
In this sense, the OED explains, “suppose” is an imperative verb meaning “assume,” “imagine,” or “what if?” However, the dictionary gives examples from the 15th to the 20th centuries of the word “passing into conj.” in Scottish English.
We’ll end with an Oxford citation from the July 25, 1907, issue of the Nation about William Jennings Bryan’s campaign for the Democratic Party’s presidential nomination:
“Suppose him the Democratic nominee, and the issue would be thrust in his face from every stump in the land. His party would have to bear the odium.”
Bryan won the Democratic nomination, but he was trounced by the Republican candidate, William Howard Taft, in the 1908 presidential election.