Hey everyone,
I have this problem with the use of "unless."
The most common use of unless means "except if." For example:
I will come unless it rains.

But there were few instances where unless only means "if." For example:
You can write about it unless it makes sense.

So how do I know in which context is unless being used? Especially if it is just a single sentence.

Thanks in advance.

Question

Hey everyone,
I have this problem with the use of "unless." 
The most common use of unless means "except if." For example:
I will come unless it rains.

But there were few instances where unless only means "if." For example:
You can write about it unless it makes sense.

So how do I know in which context is unless being used? Especially if it is just a single sentence.

Thanks in advance.

Answer

Your second example is wrong (and non-native). If we fix it, you'll understand: "you cannot write about it unless (= except if) it makes sense".