In the classic Japanese language the "h" sound was pronounced like "w", "h", and "f" all put together. The sound for the "ha", "hi", "fu", "he", "ho" evolved one way and the particles, which sounded closer to "wa" and "we", went a different route. They finally ended up taking sounds slightly different then the hiragana was normally pronounced which were also sounds already found in the Japanese language so these two exceptions are often very confusing to outsiders.