Some words end in th (length, width), and others end in ht (height, fight, tonight, caught).

I sometimes have difficulties in spelling such words because I don't know which ending to choose.
Is there any rule or pattern (even localized) in choosing one or the other?

  • 5
    Hint: -ight, not just -ht.
    – RegDwigнt
    Commented May 9, 2011 at 22:49
  • 2
    @RegDwight Interesting, I added "caught"...I just misspelled RegDwigth Commented May 9, 2011 at 23:01
  • Well, you can add even more things on top of that, but the real culprit is still gh. A good answer will point out why it's there, even though (there it is again, though) it's not pronounced.
    – RegDwigнt
    Commented May 10, 2011 at 0:02
  • very good question, dude!
    – theotheo
    Commented Sep 14, 2017 at 19:29

3 Answers 3


The first thing to note is that the two sets of words that you mentioned end with different sounds. The ones ending in th all have the [θ] sound, which is formed by putting the tip of the tongue between the front teeth and blowing. The ones ending in ht all have the [t] sound (or some allophonic variant thereof). If you're not a native speaker of English, you might have difficulty producing the [θ] sound or distinguishing it from [t], but for native speakers of English the distinction is perfectly clear, and so this problem never arises.

The secondary issue is that of spelling, as you find th and ht confusing. This is a matter of mis-parsing some common English digraphs. When attempting to read those words, you shouldn't take h and t together, but rather g and h together, as the digraph gh is pretty common in English, and is usually silent when it's not at the beginning of a word. (In a few words it's pronounced as [f].) In other words, whenever you see gh in words like this, you should completely ignore the gh, and read the words in your example as heit, tonit(e), fit(e), caut, etc. The fact that the h is next to the t is irrelevant, since the h is really part of the silent digraph gh.

A final, confusing issue is that a few words ending in -t are sometimes (mis)pronounced as if they ended in -th. For example, the word height in proper speech is approximately [hait], but it's often pronounced something like [haitθ]. This is due to influence by other words denoting qualities of measurement (length, width, depth) which all end in [θ].

  • So if we have a "g" before the last 2 letters, it is followed by "ht". Exception: "ngth" (length, strength), where "g" is not silent. Otherwise, the word ends with "th". Notable exception: yacht. I have used morewords.com Commented Nov 27, 2011 at 7:57
  • 1
    @BogdanLataianu, I think you're still fixating on an irrelevant detail. Having "g" before the last two letters doesn't mean anything at all, and pretty much anything might follow. Consider ugly, angry, begin, bragged, or any number of other things. The important thing is the combination gh, which is always silent (unless it's at the beginning of the word). Commented Nov 28, 2011 at 13:37
  • I understood your point. It then remains to be aware that the "g" in strength, length are not silent. I noticed that "ch" plays the role of silent "gh" in yacht. Commented Nov 29, 2011 at 20:25
  • FYI: regarding "length, width, depth which all end in [θ]" - see heighth, really Commented Feb 3, 2018 at 13:18
  • Thank you! For a non-native who spend most of the time reading rather than hearing English, these words have always been cumbersome.
    – SeF
    Commented Apr 21, 2020 at 9:09
  1. I think your examples are backwards.
  2. Any word ending with a -th spelling ends with a th sound

To make a th sound, trap your tongue between your upper and lower front teeth, blow gently, and release the tongue. To make a t sound, put the tip of your tongue against the ridge just behind your upper front teeth and blow gently.

I notice that sounds involving biting the tongue or lower lip are the hardest for speakers of Asian languages to get right. I think it's solely a feature of European languages. A Bangkok cab driver once offered to get me a ride in a whoa-whoa. It wasn't until he explained that it was a Swedish car that I figured out what the heck he was talking about.

  • I don't think he was talking about the sounds, but rather about the fact he couldn't remember the spelling when writing them.
    – Alenanno
    Commented May 9, 2011 at 22:53
  • Yeah, it might be a psychological effect. Since I make a dental "t" (as in my native language), instead of an alveolar, this error persists in spelling too. @Malvolio made me understand that. Commented May 9, 2011 at 23:14
  • @Malvolio I would question your method of pronouncing a t. You produced a small burst of air similar to when making a k sound, you don't blow. Very different from the blowing for th anyways. Commented May 9, 2011 at 23:15
  • @Malvolio @Matthew Read: To be exact, you block the air-flow for a moment (when the tongue is touching behind the teeth) and you release it soon after it, check this.
    – Alenanno
    Commented May 9, 2011 at 23:38
  • @Bogdan -- if I sounded intolerant, I apologize, sincerely. I don't speak (for example -- guessing from your name) Croatian at all. Like Korben Dallas (qv), I only speak two languages: English and bad English; so I respect anyone who can achieve any fluency in any but his mother tongue. Commented May 10, 2011 at 0:55

Noticed a pattern with the vowel +

e.g. weight , height and caught (vowel + g)

as opposed to

length and width (no vowel + g)

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