In the OED:
effectively, (adverb)—in such a manner as to achieve a desired result: make sure that resources are used effectively.
effectual, (adjective)—successful in producing a desired or intended result; derivatives: [...], effectually adverb, [...].
effectually [...] Synonyms: completely, effectively.
In the Encyclopaedia Britannica I read:
Though the designs of the Frenchs against Jamaica were now effectually frustrated, the victory was not followed [...].
Further, in the Guardian I read:
Schools that had once been mixed were now effectually segregated.
So, I am confused if the above sentences would sound better as
- Though the designs of the Frenchs against Jamaica were now effectively frustrated, the victory was not followed [...]
- Schools had once been mixed were now effectively segregated.
Can you confirm whether effectually and effectively are completely interchangable or not?
Note: I read "'The team is moving around really effectively.' — Is this a correct use of effectively?", but there it does not answer my question.