replying to macs2005:
The Romans brought the Roman alphabet to Western Europe. The adaptation was in many cases like trying to get a round sound to fit in a square ear.
After that, to add to the confusion, English picked up new phonemes (like the -ng at the ends of words) and lost a few (like the -gh), an artifact seen in "enough". The -gh sounded somewhat like an "f" made in the back of the mouth, and it developed into the "f" we all know. To complicate it more, there was the "Great Vowel Shift" you can search and read about, that occurred five and six hundred years ago. The vowels for the most part lost their old Roman values.
One way we learn about this is by looking at the end-rhyme of ancient poetry. For example,
God is great,
and God is Good,
we thank him for this Food.
So many times I've heard people comment, "how stupid, 'food' doesn't rhyme with 'good'." Once it did.