validity
This term carries a heavy weight of authority and precision. It is most frequently encountered in legal, scientific, and philosophical discussions where the difference between a truth and a falsehood must be definitively proven. It suggests a binary state: something is either valid or it is not, leaving little room for ambiguity. In a psychological or research context, it refers to the accuracy of a measurement. If a test has high validity, it means it actually measures what it claims to measure, rather than some unrelated variable. This distinguishes it from reliability, which focuses on consistency rather than truth.
Uncountable when discussing the abstract quality of being true or sound. Countable when referring to specific instances of legal effectiveness, such as the various validities of different documents in a case.