Number 2 and 4 do not sound natural. So I suppose you can come to the conclusion that you should generally avoid using 'unless' with (B) "unless you don't do that." The second part of the sentence should generally be "unless you do that." "I'll starve unless you eat." "I won't eat unless you eat" These sound fine. But you don't say "I'll starve unless you don't starve." or "I won't eat unless you don't starve." I mean you can but it will confuse the listener and have to process it. It doesn't flow. Normally when you use 'unless' it's because you want an affirmative action from the other person. You are giving them an 'ultimatum' because you want to make them DO something. "I won't cook your dinner unless you clean your room." "I won't buy you flowers unless I get a kiss." (playful example) "I won't stay with you unless you buy me flowers." (playful response lol) or "I'll run away unless you buy me flowers." All have to end in an affirmative action, it doesn't matter about the first part. So if you are thinking of using 'unless', but you find you are stuck because you have a construction like "I'll do this/won't do this unless you don't do that" then, just flip the last part into an affirmative action. Instead of saying to your friend, for example, "I won't talk to you unless you don't be an idiot," You can just say "I won't talk to you unless you behave." If they answer what do you mean 'behave'? Then you can naturally answer, "stop being an idiot/stop insulting me/ etc any other example." Hope this helps.

Hi, These are logically constructed sentences, but if you used some of them with native English speakers they might struggle to understand what you meant. They would certainly ask you what you meant. 1- (A) I'll do this unless (B) you do that. I will do this if you do that 2- (A) I'll do this unless (B) you don't do that. As long as you don't do that, I will do this. 3- (A) I won't do this unless (B) you do that. If you do that, then I won't do this 4. (A) I won't do this unless (B) you don't do that. If you don't do that I won't do this

This is a tough question. I can't think of any examples that would match the format of examples 2 or 4...it sounds very odd. Try to think of the definition of the word rather than the grammatical technicalities. So "unless" is referring to something that is conditional, the definition being "except under the circumstances that" So, you could say, "I won't go to the grocery unless you give me money." or "I'll go to the grocery unless you don't give me money." But, if I said, "I won't go to the grocery unless you don't give me money." *technically* that might be grammatically correct, but you are getting into a realm of double negatives and the meaning is unclear...so nobody speaks that way. And saying "I will go to the grocery unless you give me money" changes the meaning, to mean that you will go, but if you give me money I'll do something else. So basically, stay away from the double negatives, and keep the definition of the word in mind. Also, as far as speaking is concerned, no one really says "insofar as" so I wouldn't really worry too much about that unless you're writing a lot of formal papers. And "to the extent" just means that there is a limit to whatever you're saying and what you are talking about is included up to that certain point...not sure if that makes sense.

Thank you Lee! Very concise and clear

I would say the UNLESS clause should have a POSITIVE verb to sound most natural. The other clause can be positive or negative. I won't go unless you do. (negative) (but I'll go if you do) I'll go unless you want to go instead. (positive)