To be "infirm of purpose" is to be at the mercy of the artful or at the disposal of accident.
If she fell, should he not save his friend from being the dupe of an artful intriguante?
Is incensed against him for his artful dealings with her, and for his selfish love.
She raves at him for the artful manner in which he urges Clarissa to marry him.
A preconcerted, forward, and ...