If somebody makes a condition against the laws of the Torah, the condition would not be valid. For example, let's say a man tells a woman that he wants to marry her, but only on the condition that they do not have any marital relations. We know there is an obligation from the Torah for a husband to provide his wife with marital relations. Therefore, the whole condition is not valid, but the legal act does take effect. In that case, the condition is gone. Obviously, the husband and wife could engage in marital relations, but they are still considered married. It's like the condition was never said because it's nonsense. You can't make a condition that goes against the laws of the Torah. So the condition is wiped away, but the rest of the statement continues to happen.
We're called to...
Any condition where the action associated with it is mentioned before the actual condition is not a valid condition. For example, let's say a man tells his friend, "I'm going to give you this gift under the condition that you walk 20 miles." The action—the giving of the gift—is mentioned before the "if," before the condition. So in this case, we separate the statements. He says, "I'm going to give you a gift," and we isolate that, and he has to give him the gift. He's giving him the gift. The condition that's said afterward does not apply, and the condition is not valid. The only way the condition would be valid is if it came first. If he says, "If you walk 20 miles, I'm going to give you a gift," that "if" has to be mentioned before the action of what he wants to do if it all happens.
If a condition is possible to eventually fulfill, and the one making the condition said it at the beginning, before he said the action, like we just learned in the last part of the Mishnah, it's a valid condition. But if the condition was impossible to actually fulfill, or if the action, like we just learned, was said first, then it's not a valid condition. Let's say, for example, he said, "If you jump up to the moon, I'm going to divorce you." Here, he said the "if" first, the condition first. The problem is that the condition was something impossible. It's not possible for a person to jump up to the moon. Therefore, we say that the woman is divorced without that Tenai (condition). The Tenai is fully ignored. And therefore, we assume that he did not mean the Tenai as something serious. The action he was saying would happen does happen even without that condition.