I've noticed that in particular germanic languages have similar base words to english of which many times the only difference is that of the vowels. This would make sense seing as to how they are descended from the same language, but really what I'm wanting to know is whether or not there is a discernable pattern between english and one of these germanic languages. I have looked mainly at icelandic words and have found there to be a bit of a pattern or at least some basic rules which it seems to follow. For example, in from an icelandic to english compairison, A, O, E, and U will sometimes "turn into" an A in english, but only an E, or I will continue to be or turn into an I in english.
I have only checked some of the most common icelandic words, and some of the compairisons are a bit of a stretch as to how well they can be, in essence, transliterated. For example, the icelandic word, "með," meaning with, was a word I used to count as an exapmle of the icelandic E turning into an I. Additionally, since icelandic doesnt descend from english and vice versa, I don't know how well they can be compared since they have evolved differently and share less in common than english would with german or even another germanic language such as dutch.
What really I am asking is whether there is a pattern between certain words based off of their phonology or morphology that once can better use with germanic languages to be able to "predict" better what a word might have derived from.