1. From a general law to a particular instance; valid independently of observation.
2. Existing in the mind prior to and independent of experience, as a faculty or character trait.
3. Not based on prior study or examination; nonanalytic: "He made an a priori judgment."

The term a posteriori has the opposite meaning: from particular instances to a general principle or law; based upon actual observation or upon experimental data and not existing in the mind prior to an experience.