"Causatively" refers to the way something has been caused or brought about. If you are looking for synonyms for it, you might wish to use words such as "origination", "initiation", "inducement", or "instigation". These words can help you to convey a similar meaning, expressing how something has been set in motion or started. "Precedent", "basis", "reason", and "source" may also be useful alternatives to causatively, depending on the context. It's worth exploring different synonyms to find the one which most accurately reflects the intended meaning, and which fits in with the tone and style of the text being produced.