The word "presupposal" is a fairly uncommon term that describes something that is assumed or taken for granted. If you need to find synonyms for this word, you can go with simpler terms like presupposition, premise, assumption, or supposition. Other potential options include preconception, impression, notion, or hypothesis. Depending on the context of your writing, you may also be able to find more specific synonyms such as prerequisite, requirement, or precondition. Ultimately, the choice of synonym will depend on the tone and complexity of your writing, as well as the nuances of the idea you are trying to convey.