No, person saying this, you probably don’t. You most likely have a hypothesis. While I don’t go around correcting people when they say “I have a theory” when they most obviously do not have a theory, I do correct them in my head, because they’re wrong. I don’t correct them because I know what they mean, and since the meaning isn’t lost, there’s no need to correct them. Having said that, dear reader, there is a difference between theory and hypothesis:
A hypothesis is either a suggested explanation for an observable phenomenon, or a reasoned prediction of a possible causal correlation among multiple phenomena. In science, a theory is a tested, well-substantiated, unifying explanation for a set of verified, proven factors. — Google definition
In other words, a theory has science behind it, research and study. A hypothesis is an educated guess. Most of the time when someone says, “I have a theory.” They’re saying, “I have an idea.” or a guess. I can almost bet money that they have not done much (funded, scientific-type) research, and that there’s little to no science to back up their claim. Like I said though, I don’t correct people when they say, “I have a theory.” because there’s no need to. In the popular vernacular, theory means the same as hypothesis and that’s just how language works.
Let me explain: it used to burn my buns when someone used the word alternate for alternative as in “Should we make alternate plans for tonight in case Susan doesn’t show?” Because alternate is a verb — “I have to alternate between the chair and the couch because of my bad back.” and alternative is an adjective (or noun) – “If you have an allergy to something on the menu, we can offer an alternative selection.” But, now alternate is accepted as an adjective and a substitute for alternative — an alternative for the word alternative if you will. ^_^ At least it’s accepted as such here in the United States. I dunno about anywhere else. So my getting heated up didn’t do anything to change it. And correcting people left and right about the “proper” usage didn’t stop it. It’s just how language rolls. It changes. It will always change. Nothing anyone does will stop it from changing. It was this very thing here that opened my eyes to just how fluid language can be. Well, one of the things. A few things happened at the same time, but they all coalesced into an epiphany and I just stopped correcting people. Life for me got a lot easier when I did.
Now, if y’all will excuse me: