The conjunction “unless” alters the meaning of a conditional clause by indicating a condition that must not occur for a situation or result to happen. It introduces a situation where an exception or negation to the condition set in the clause is implied.

For example:

– “I will go for a walk unless it rains.” (Meaning: I will go for a walk if it doesn’t rain.)

In this sentence, the condition for going for a walk is that it must not rain. If it rains, the situation changes, and the walk won’t happen.

“Unless” functions similarly to “if not” or “except if” in expressing the idea of a negative condition. It is used to present an alternative scenario in which a specific condition is not met. The presence of “unless” in a conditional statement can significantly impact the structure and meaning of the sentence by indicating the necessity of avoiding a particular condition for the main action or outcome to take place.