The History of Lenition in Irish Gaelic

After definite article, after certain procltics, there is initial lenition. In the nominative singular, like the woman for feminine, you have a lenition of that initial consonant. For masculine's, you don't. So, it's an interesting kind of, uh, lenition process there that has to do with both the case and the gender of whatever the object or the thing was. And there has to be a historical explanation.