Silent letters are often found within the english language.  They occur not to be difficult or to make spelling harder, but because of their history.  The english language is a very old language and has its origins based across many other languages, ways of spellings and pronunciations.

In the past there were many different rules on how to speak a word, and as an example,  word ending in 'e' had a variety of possible pronunciations.

Over the centuries the rules pronunciation have changed and become easier.  But this means that some of letters used over that time no longer have a purpose, and are simply not used.

Until the introduction of the printing press in 1476 many silent letters 'fell off' the word.  However the printing press made language more standard and stable and therefore most spelling have remained in place, even if the pronunciation has changed.

For example:  knight has German origins and both the 'k' and 'gh' sounds are not pronounced in english.

Tsunami is Japanese but the 'ts' sound is difficult for the english speaker to say and has therefore been shortened to 's'.

Many words beginning 'ps' and 'pn' have Greek origins, and the 'p' usually remains silent as in psychology or psoriasis.  However some words are beginning to transition for example pneumatic can occasionally be seen as neumatic.

Silent B

B is not pronounced when following M at the end of a word.

climb

crumb

dumb

comb

Silent C

C is not pronounced in the ending "scle" - muscle

Silent D

D is not pronounced in the following common words: handkerchief, Wednesday

Silent E

E is not pronounced at the end of words and usually makes the vowel long.

hope

drive

gave

write

site

Silent G

G is not often not pronounced when followed by an N

champagne

foreign

sign

feign

Silent GH

GH is not pronounced before T and at the end of many words

thought

through

daughter

light

might

right

fight

weigh

Silent H

H is not pronounced when following W. Some speakers whisper the H before the W.

what

when

where

whether

why

H is not pronounced at the beginning of many words. Use the article "an" with unvoiced H. Here are some of the most common:

hour

honest

honor

heir

herb

Pronounced H

is pronounced at the beginning of these common words. Use the article "a" with voiced H.

hill

history

height

happy

hangover

Silent K

K is not pronounced when followed by N at the beginning of a word.

knife

knee

know

knock

knowledge

Silent L

L is often not pronounced before L, D, F, M, K.

calm

half

salmon

talk

balk

would

should

Silent N

N is not pronounced following M at the end of a word.

autumn

hymn

Silent P

P is not pronounced at the beginning of many words using the suffix "psych" and "pneu".

psychiatrist

pneumonia

psychotherapy

psychotic

Silent S

S is not pronounced before L in the following words:

island

isle

Silent T

T is not pronounced in these common words:

castle

Christmas

fasten

listen

often

whistle

thistle

Silent U

U is not pronounced before after G and before a vowel.

guess

guidance

guitar

guest

Silent W

W is not pronounced at the beginning of a word followed by an R.

wrap

write

wrong

W is not pronounced with these three pronouns:

who

whose

whom