na-adjective
hypothetical
Used to describe something that is based on a hypothesis or assumption, often in academic or logical contexts. Not a common everyday word.
その議論は仮言的な前提に基づいている。
That argument is based on a hypothetical premise.
仮言的な状況を想定して対策を考えた。
We considered countermeasures assuming a hypothetical situation.
仮説的 is a more common adjectival noun for 'hypothetical', especially in scientific contexts. 仮言的 is rarer and more formal.
Compound of 仮言 (kagen, 'hypothesis' or 'conditional statement') + 的 (-teki, '-like'). The exact historical derivation is uncertain, but it follows a common pattern for forming adjectival nouns from Sino-Japanese nouns.