This paper is dedicated to English language. This topic was chosen because it is interesting.
As we know, there are great communities of languages, called families. Most European languages and several Asian belong to one of the families, Indo-European (exceptions are Hungarian, Finnish, Estonian, Karelian, and Livonian, which are Uralic). English is certainly one of them.
Languages of any group are distinct because of divergence. This is a process when a language splits into several: people who formerly spoke one language stop to understand each other. Of course, it takes long time i.e. hundreds and thousands years. So protolanguage may split several times. As a result, a lot of modern speeches are related to few protolanguages.
When first Europeans came to India, they found that Indian speeches are like old European ones, especially Latin and Greek. So Indo-European family was discovered, but its existence wasn't proved enough. One of philologist, August Schleicher, noted that divergence has its own laws, and discovered some phonetical relations. Thus he was able to re-create some words and grammar of proto-Indo-European language. He thought he would finish the re-creation and wrote a fable, A Sheep and Horses, in "new" language. Although, he made some mistakes. New generation of Indo-Europeanists corrected them, but doesn't even try to write something, because it is impossible to re-create everything.
According to Schleicher, at first subfamily of Germanic, Baltic, and Slavic split from their relatives. As calculated later, it was about 7000 years ago. Then Germanic separated from Balto-Slavic. This means that proto-Germanic went under changes, which made it different. These changes are known as Grimm's law or Verner's law.
Unvoiced stops became voiceless fricatives: pàf, tàth, kàh;
Voiced stops became unvoiced: dàt, bàp, gàk;
Aspirated stops became non-aspirated.
This is Grimm's law. Verner law is more specific.
When Angles and Saxons (and Jutes and Frisian) (which were Germanic) came to the Great Britain, they met Celtic (particularly Britts) people. So, Old English is primarily Germanic language with Celtic buries. (Including such words as down). Old English grammar was difficult enough; it is the reason why it was simplified in Middle English period.
The period began after Norman Conquest (1066). French became the dominant language, so English grammar changed, and many words were buried. Some scholars believe that English is German-Roman language (not just Germanic), and some do not accept it. Latin alphabet was used instead of runes (a specific writing of Germanic) even earlier, but Norman suggested new orthography.
The last step of the language is called Modern English. It began with Great Vowel Shift. However, orthography remained; so pronunciation became different from spelling. The shift began in 1350 or 1500 (more exactly) and finished about 1600. The shift caused convergence of some sounds. As a result, spelling of Modern English is so difficult, as you know.
Thus neither consonants nor vowels in English words do not match with their origins, but there is a set of rules which helps you to re-create protolanguage words.
L i s t o f L i t e r a t u r e:
1. Funk & Wagnalls Encyclopedia, 1993
2. Schleicher, August. Compendium der vergleichenden Grammatik der Indogermanischen Sprachen, 1862
3. Webster, Noah. Third New International Dictionary, 1981