Three-letter rule?

I bet you weren’t taught this at school.

Look at these pairs of words

in ............. inn
to ............. two
or ..............oar
I ............... eye
no ............ know

Did you notice:
Do the words in each pair have

  • the same sound?
  • the same meaning?
  • the same spelling?

How long are the words in each column?
What kind of words are in column A) and in column B)?

These word pairs are all homophones so they sound the same but the meaning and spelling are different. You will see that in column A) all the words have one or two letters only. In column B) they are at least three letters long. In column B) we find only ‘content’ words – usually nouns, verbs and adjectives which carry clear meaning – and in column A) we have ‘function’ words. - the words we use for grammar.

Vivian Cook, in his excellent The English Writing System, claims that “content words must have more than two letters” These ‘rules’ always worry me, but it does look like it’s generally true, though it may be better to say “words that can only be used as content words must have more than two letters”. ‘Go’ can be a content word (“I want to go now”) or a function word (“I’m going to get fit next year”). There are very few other content words with two letters in common use.

Interesting that!

Read more by Vivian Cook:
His website:
The English Writing System by Vivian Cook. Published by Arnold (2004).
Accomodating Brocolli in the Cemetary by Vivian Cook. Published by Profile (2004)


  1. Searching a 60,000-word list, I find the following 2-letter content words:

    ad (advertisement in American English)
    ax (variant spelling of axe)
    do (when used as a main verb)
    em (size of a capital M in a typeface)
    en (size of a capital N in a typeface, half an em)
    ex (in the sense "ex-spouse")
    fa (solfegge note)
    ki (see qi)
    id (Freudian psychology)
    mi (solfegge note)
    op (short for "operation", usually plural)
    pi (either the Greek letter, or mis-set type)
    qi (Chinese spiritual energy)
    ti (solfegge note)
    xi (Greek letter)

    That makes 19 words out of 65, or 29%. So the "rule" doesn't even work 80% of the time.

    (There are also the proper names Ab (for Abner), Al, Av (Jewish month), Ed, Jo, Ob (Russian river), Oz, Ra (Egyptian god), and Ur (former city in Iraq).)

  2. Sure, John, there are more two-letter words (as I was writing this posting I predicted comments like this) and I'm sure seasoned Scrabble-players could find more. Thank you for taking the time to dig these ones out, but I'm sure you will agree that most of them are either pretty rare (several there I've never written in my life!), abbreviations, or as I mentioned in my posting, words that are not only used as content words (like 'go' and 'do'.

    I'm keen through this blog to try to help people who struggle with English spelling (particularly non-native speakers) to improve. And to help their teachers too. If we can identify some patterns that may help them then great. Sure, we can always find exceptions - that's why I prefer to explore patterns that already exist rather than try to force spellings into unhelpfully complicated rules. The patterns I talk about are not 100% watertight - they are not supposed to be, but if they help someone remember the difference between 'by' and 'buy' - great!

  3. With the exception of by/buy and no/know kids don't usually mix these words at all. This can be helped with an explanation about knowledge/knowledgeable vs no/not/nothing/none. I made visuals for my class last year on this topic. I also pointed out that nose is not related to either. Nose is related to nostril and nasal. That could have been stretching it but the nose pictures were funny. I then asked students to create cartoons to demonstrate understandings. btw my students are 9-10 year old Aussie school kids including many ELLs.

    I have not made a similar one for by/buy but one day now...