Are there synthetic propositions known a priori?
Whether it is possible for a synthetic proposition to be a priori is a matter of considerable controversy in philosophy. The empiricists hold that there are no synthetic a priori truths. The rationalists hold a contrary view – that there are synthetic truths that are also a priori. In rationalist view, certain concepts are derived from experience – but once these concepts have been derived, they are seen as necessarily true. For example, in this view, we derive the notion that 2 + 2 = 4 from experience – it would not have occurred to us had we not experienced two things, and another two things, becoming four things – but once we do experience it, we recognize it as a necessary truth.
