There are lot of silent letters in English language . Pronunciation of different words is different and there is no rule for silent letters, Spelling of silent letters is a problem for native speakers as well as non natives.
“In an alphabetic writing system, a silent letter is a letter that, in a particular word, does not correspond to any sound in the word’s pronunciation. Silent letters create problems for both native and non-native speakers of a language, as they make it more difficult to guess the spellings of spoken words.
Phonetic transcriptions that better depict pronunciation and which note changes due to grammar and proximity of other words require a symbol to show that the letter is mute”.
Source: http://en.wikipedia.org
