When to Pronounce Final h (and when not to)

You're in for a shock here I'm afraid - the rule is simple. But, at first glance, it can be confusing to recognize when a final [h] (usually represented by th in the spelling) is pronounced and when it's not. The surprisingly simple rule is that when you have the final letters (like th) indicating a final [h], you pronounce the [h] if it's at the end of a monosyllabic word - that is, if the word has only one syllable and if the preceding vowel is short. Remember that a diphthong counts as a long vowel!

Note that even if the [h] is pronounced it tends to be relatively weak and often disappears in normally fast speech, but more of that later.

Soo ... let's look at some contrasting examples:

cath	⇨ [kah]
bùth	⇨ [buː]
gath	⇨ [gah]
bàth	⇨ [baː]
tuath	⇨ [tuə]
mòrghath	⇨ [moːrɣa]

Having a longer word ending in -th is actually very rare, so the issue of counting syllables goes away for the most part anyway.

Ok, someone asked whether that doesn't mean that bàth "drown!" and bà, the genitive of "cow" aren't pronounced the same way and make life confusing. Actually, yes and no. Yes in the sense that they are pronounced the same way. No in the sense that it doesn't make life complicated. For one thing English has much more of the same - think of [naɪt] and [naɪs]. You tell me whether those two are "night" and "gneiss" or "knight" and "nice"! And the other two reasons are word order and context. In Gaelic you'll never get the word [baː] "cow" in the same position as you might get the word [baː] "drown!" as the first is a now and the second a verb. Plus there is always the ever helpful thing called context which usually clears up any confusion. No language has no ambiguity because we couldn't pun otherwise!

So what was that about fast speech? Well, this final [h] is just one of those things that tend to disappear when you speak normally. There's more on fast speech to be found here.