The key thing to remember is that English is a language of many sources.
Up to 50% of our lexicon is derived from French, thanks in large part to the Normans. The rest of our modern lexicographic and syntactic makeup has roots in Anglo-Saxon (Old English), Latin, and Scandinavian language. In the Middle Ages, it was far more fragmented and actively mixed, but as things became more homogenized, the language came to be known as Middle English, then Elizabethan English, then Modern English. As the language progressed, it became less evident where the words and structure came from. This is why most of us are impressed to find out that we use far more French than we think...or, at least, anglicized forms of French. For example, anytime you use a word ending in -tion/-sion, -ence/-ance, or -tive, it will most likely be a word derived pretty much directly from French, if not from Latin through (Old) French.
Given this as the source of our language, it should come as no surprise that there are some rather interesting inconsistencies, many of which go beyond pronunciation. Ask anyone who has learned English as a second language and they will probably tell you they had their moments that caused them to scratch their heads.
Things then get really confusing when you look at the language's regional differences.
