Η εκ των υστέρων γνώση προέρχεται από την εμπειρία. Είναι γνώση εκ των υστέρων. Ξέρεις ότι ο ουρανός είναι μπλε επειδή τον έχεις δει. Ξέρεις ότι η φωτιά είναι καυτή επειδή την έχεις νιώσει. Η γνώση εξαρτάται από αισθητηριακά δεδομένα. Χωρίς εμπειρία, δεν θα την είχες.

The term is Latin for from the latter. It contrasts with a priori knowledge, which is independent of experience. A posteriori knowledge is empirical. It is based on observation, experiment, and evidence. Science is largely a posteriori. It tests hypotheses against the world. The results are known only after the experiment.

Examples of a posteriori knowledge

• The boiling point of water is 100 degrees Celsius at sea level.
• Paris is the capital of France.
• Some swans are black.
• Pain feels unpleasant.
• The law of gravity holds on Earth.

A posteriori knowledge is contingent. It could be otherwise. The boiling point of water could be different on another planet. Paris could have been a different city. Black swans exist, but they might not have. A posteriori truths are discovered, not deduced. They require investigation. They are always open to revision. A new observation can overturn a posteriori knowledge. That is the strength and the weakness of empiricism. It is grounded in reality, but it is never certain. The next experiment might change everything. A posteriori knowledge is the knowledge of the world as it is, not as it must be.