1. an idea or theory that is believed to be true but is not proven
2. the act of supposing or assuming something

Examples

• Her theory was based on the supposition that all students learn at the same rate.
• The detective’s supposition about the crime proved to be correct.
• We can proceed on the supposition that the weather will improve.
• His argument rests on the supposition that people are naturally good.
• The supposition that technology always improves life is questionable.
• Without evidence, your claim remains mere supposition.