Vice, by comparison with terrible accidents, has its own peculiar explanation. For, in a way, it does occur in accordance with the rationale of nature, and its occurrence is not, so to speak, useless in relation to the whole world. For otherwise, the good would not exist, either.
Of causes, some are complete and primary, others auxiliary and proximate. Hence, when we say that all things come about through fate by antecedent causes, we do not mean this to be understood as 'by complete and primary causes,' but 'by auxiliary and proximate causes.'
If something were brought about without an antecedent cause, it would be untrue that all things come about through fate. But if it is plausible that all events have an antecedent cause, what ground can be offered for not conceding that all things come about through fate?