speculate about (someone or something)
To conjecture, hypothesize, or make guesses about someone or something without having supporting or conclusive evidence. We've all been speculating about the mysterious man who moved into the house two doors down. It's certain to be a gamble, but until we try it, all we can do is speculate about how the product will do on the market.
speculate about someone or something
to make guesses about someone or something; to hypothesize about someone or something. I refuse to speculate about Sally. I don't presume to guess what she will do. We don't speculate about the future.
speculate in something
to make risky business deals in the buying and selling of something. Jeff made a fortune speculating in cotton. I do not wish to speculate in anything. It is too risky.
speculate on something
to make a hypothesis about something. I really don't want to speculate on what might happen next. Would you care to speculate on what might happen if you quit your job?