母音変化は「母音三角形」で説明されますね。舌が前の方で段々上顎に盛り上げていくと〈 a → e → i 〉となるし、 舌が後ろで段々盛り上げていくと〈 a → o → u 〉となる。 サンスクリット語では母音を強調すると [ i → e ]・[ u → o ] となり、これを「guṇa saṃdhi」(saṃdhi:連声) と呼び、更に強調すると二重母音化して [ e → ai ]・[ o → au ] となり、これを「vṛddhi saṃdhi」と呼んでます。
Got randomly recommended this at least three times now. I enjoy linguistics, but i don't understand japanese. I have no idea of what the hell is going on but i may as well tag along for the ride. EDIT: Ah, indo-european
English is very much Germanic. It has only few Celtic influences. Most foreign influences are from Norman-French. French has a lot of Celtic influence, but not as much as Germanic.