CAMBRIDGE, Mass. — THE conventional wisdom about Syria is that nothing can be done. It is said that military action would be either perverse — bringing the jihadists in the opposition to power — or futile, failing to tip the balance against the government of President Bashar al-Assad. Using force, it is argued, would also jeopardize other strategic objectives, like securing a lasting nuclear deal with Syria’s supporter Iran.

The trouble is that the conventional wisdom may be fatalism parading as realism and resignation masquerading as prudence.

Any realist needs to face two facts. First, absent the credible application of force against the Syrian regime, a negotiated transition leading to Mr. Assad’s departure is not going to happen. Despite the efforts of the United Nations envoy Lakhdar Brahimi, the peace talks in Geneva between the Syrian government and the opposition coalition have become a waste of time. The opposition forces have been weakened by military defeats, and Mr. Assad’s strategic advantage gives him no incentive to concede anything.

Second, if Mr. Assad is allowed to prevail in this conflict, he will reimpose his tyranny, and his forces will surely exterminate the remaining Sunni insurgents who make up most of the opposition. Obliterating his enemies, however, will not bring lasting peace. It will only further inflame hatreds. Sooner or later blood will flow again.