Why do words have "silent" letters?

[islasmum]

For example

Knee
Pneumonia
Knight
Knive
Gnat

and so on?

[mike11111]

Because they derive from other languages and the initial letters were originally sounded, they were not originally 'silent'.

[fbg40]

It's the same as the "P" in bath that's silent !
FBG40

[Old_Geezer]

It's to keep you on your toes.

I suspect whoever wrote the first dictionary (Johnson ?) was overwhelmed by the task and made a right screw up of the official English spelling that they defined. Had they kept to a few simple rules we'd all accept it now.

[rojash]

Can't answer for the others, but pneumonia is from the Greek (pronounced pnevmonia - the "u" is actually ypsilon, which is pronounced f or v after a vowel other than o). In Greek, the p is not silent.

Words beginning ps (such as psychiatrist) are also from Greek, and the ps represents the single letter psi in Greek - so once again, the p is not silent.)

[Quizmonster]

Knight came from German and Dutch Knecht, with the 'ch' as in Johann Sebastian BaCH, meaning a servant. I'm sure you wouldn't want us to pronounce it as it was in Monty Python's 'Holy Grail' which was, roughly, kinniggit!

[douglas9401]

Well in that case Quizmonster, I fart in your general direction. :)

[tearinghair]

My maiden name was Knight, and when I lived in France for a while my landlady referred to me as 'Miss K'nisht'.

[islasmum]

Thank you all for your interesting and informative answers (especially fbg40 - although that might possibly be classed as "too much information"!)
No wonder English is a difficult language to learn, not only the silent letters, but so many word have more than one meaning. It's all very interesting.

[Quizmonster]

I hope, Douglas - if you mean to carry out your threat - that you are an unladen African swallow!
I always heard that the silent 'p' was in sea-bathing, but I guess bathing anywhere is as relevant.

[THECORBYLOON]

Why do we sound the "h" first in "wh" words?

[MarkRae]

In fact, compared to other languages, English is one of the easiest languages to learn up to a basic level of fluency - we have no gender of nouns (e.g. le lapin, la vache etc), we no longer make the distinction between informal and formal second person singular (e.g. tu and vous in French), meaning is not lost if we use the wrong tense of the verb (e.g. yesterday I go school and learn things). What the government terms "basic English" contains less than 1,000 words.

However, English is one of the hardest languages to learn to speak well. Typically, learners have huge difficulties with our phrasal verbs e.g. look in, look out, look after, look forward, look back etc.

[THECORBYLOON]

^^ Not in the case of "who" but the likes of "where" or "whale" for example.

[MarkRae]

^^ Definitely! Where and wear, whale and wail are not pronounced the same.

[Quizmonster]

TCL is clearly of Scottish 'background' as am I. His point, I imagine is that most English speakers tend to pronounce whales and Wales in the same way, whereas most Scots make a clear differentiation as regards the opening 'wh' sound.
Chambers Dictionary recognises this by first putting an 'h' in brackets in its pronunciation guide for whale. Their view seems to be that you are free to start with an 'h' OR a 'w' sound. In Old English, whale was hwalas, so at one time we DID put the 'h' first and the Pronunciation guide in the OED lists only that form.
My apologies if I have misunderstood your point, TCL.

[THECORBYLOON]

Yes QM. that is the point I was making. I'd not thought to look in the Chambers Dictionary for the origin. It is odd that the change was to reverse the "HW" and then for most English folk to ignore the "H" rather than drop the "H" altogether.

[heathfield]

The 'H' in many words is included to show that the consonant next to is it aspirated, or breathed. As QM points out, in olden times, the 'H' usually came first. You can blame the Norman invasion for many of the differences between spelling and pronunciation in modern English. Take the words 'enough', and 'plough'. Originally, 'enough' would have been pronounced as 'ee-now-gh', with the 'gh' sounding like the 'ch' in Bach, but more gutteral. And 'plough' would have rhymed with it. The Normans couldn't pronounce this 'gh' sound, and so under their influence it became modified. But something of the old pronunciations still exist in parts of Scotland. Even today, a farmer describing land as being 'rough' may be heard to describe it as 'rawch', with the 'ch' as in Bach.

[mike11111]

When I first started to teach myself Welsh a few years back from a textbook and not having a native speaker to help, I had great difficulty in trying to pronounce the simple word "nhw", meaning they. Fortunately the internet came to my rescue by telling me that if I wanted to be particularly affected I should pronounce the h first but to all intents and purposes I should just think of the Scottish word for "now".