A Priori vs. A Posteriori Knowlege

A Priori Knowledge:

• A priori knowledge is knowledge that we can have "prior to experience". We don’t need to observe how the world is to have such knowledge. We can arrive at such knowledge through reason alone (sitting in our armchairs by the fire, as it were, and simply using our powers of reasoning).
• Examples: "All bachelors are unmarried", "All triangles have three sides."

A Posteriori Knowledge:

• A posteriori knowledge is knowledge that we can have only after we have certain experiences. We have to make some observations to gain such knowledge. (We can’t just reflect from the armchair, we have to go out in the world and see how things actually are.)
• Examples: "There is a cup on this table", "Smoking causes cancer."