Obviously if any actions, even a lunatic's, can be causeless, determinism is done for.

If the chain of causation can be broken for a madman, it can be broken for a man.

But my purpose is to point out something more practical.

It was natural, perhaps, that a modern Marxian Socialist should not know anything about free will.

But it was certainly remarkable that a modern Marxian Socialist should not know anything about lunatics.