It seems, prima facie, that A is true. But if we suppose that A is true, then it follows that B is false.
The above argument is based on a hypothesis. The argument is not firm but prudent and tentative. Is there any word or phrase for such sort of argument?
speculative
adj.
a. Given to, characterized by, or based upon speculation or conjecture, not based on fact or investigation
As in:
The argument put forth is speculative at this point, awaiting either affirmation or refutation.
adj.
1 : dependent on or conditioned by something else
* Payment is contingent on fulfillment of certain conditions.
* a plan contingent on the weather
In philosophy and logic... (a) contingent proposition is neither necessarily true nor necessarily false. Propositions that are contingent may be so because they contain logical connectives which, along with the truth value of any of its atomic parts, determine the truth value of the proposition. This is to say that the truth value of the proposition is contingent upon the truth values of the sentences which comprise it. Contingent propositions depend on the facts, whereas analytic propositions are true without regard to any facts about which they speak.
Also,
Provisional - "arranged or existing for the present, possibly to be changed later."
Preliminary - "denoting an action or event preceding or done in preparation for something fuller or more important."
Hypothetical, either as a noun or an adjective works:
involving or being based on a suggested idea or theory : being or involving a hypothesis : CONJECTURAL
Merriam Webster
