Broad vs Slender

Depending on how long you've been doing Gaelic, you have probably come across the "Golden Rule" of Gaelic, caol ri caol is leathann ri leathann - broad with broad and slender with slender. You will probably also have learned that there are vowels which are considered broad and some which are considered slender and that the same applies to consonants.

But what is this broad and slender business really about? Well, the short answer is that e and i or sounds surrounded by them are considered slender and a, u and o and sounds surrounded by them are considered broad. For example, in aba [abə] all three letters are broad (letters mark you, we'll get to why this is important further down). In seinn [ʃeiNʲ] on the other hand, all four letters (nn counts as one letter) are slender because they are or are surrounded by e/i vowel letters.

The long answer is, well, longer. Fundamentally what is happening here is that Gaelic (and Irish and going further back, Old Irish) have two sets of consonants which linguists tell us are palatalised and velarised consonants. So we have [k] ~ [kʲ], [g] ~ [gʲ], [s] ~ [ʃ] and so on.

But why? What's wrong with just one set you might ask? The reason for this lies in the way our mouth works. When we speak, we run sounds into each other, one sound affects the next, or the previous one. Soo ...

Imagine that (very) Old Irish only had one set of consonants - [b d g f k l m n r s t]. Now take the basic vowels that we most likely had in Old Irish: a u o e i and their long counterparts. There are many ways by which you could group these but the grouping that is important for us is one of front vs back. Say [e] & [i] ... notice how they are both made at the front of your mouth? Now say [a] [u] and [o] - notice how these are made further back in your mouth? That is what we mean with front vs back.

Now one of the few iron-clad rules of linguistics is that no language, no matter how mad, can make do with only consonants. We always have at least 1 vowel. Abkhaz for example has 50 or so consonants but only 2 real vowels. So we get sequences of vowels and consonants in (very) Old Irish. Now these sounds interfere with each other. Let's look at an example:

[kenːos]	"normal/basic sounds" [k] [e] [nː] [o] and [s] Now the fun part starts. Thrown in together, these pesky little vowels start affecting the consonants ...
[kʲeNːos]	because it is followed by a front (=palatal =slender) vowel, your tongue anticipates this and instead of making the [k] where you'd make it in English (at your velum), it moves forward a bit towards your palate. The [nː] has been dragged back and changed to [N because it is followed by a back (=velar =broad) vowel. The [s] in the -os ending hasn't changed because the only vowel around is the [o] preceding it and that's back (=velar =broad)
[kʲeNː]	Now we lose the ending, just because ... but because the ending has already fixed the [Nː] as being broad, it remains broad. Enter the medieval monks which decide they want to write Irish. Hard pressed with only 14 consonants in the Latin alphabet and over 50 sounds in Old Irish which all need writing down they come up with something that is pure genius. They realise that Irish has this "grouping" where Group 1 is generally surrounded by vowels of Group 1 and vice versa with Group 2. So they more or less set down a rule saying that a consonant which is surrounded by Group 1 vowels (e i) will be a Group 1 consonant in terms of pronunciation and a consonant which is surrounded by Group 2 vowels (a u o) will be a Group 2 consonant in terms of pronunciation. Oh, they also figured that you can show a long vowel by sticking a line over a vowel and that you can show a long consonant by writing it double. So where does that leave us? 2 x 11 consonants = 22 +5 doubled consonants = 27 +5 vowels = 32 +5 long vowels = 37 +8 lenited consonants by placing a dot above = 45. Which gets us much closer to our target of 50 or so. And suddenly we can write Irish.
cenn [kʲeNː] ⇨ ceann [kʲeNː]	Hm, a bit messy still because you can't really tell from the spelling whether the nn is broad or slender. So what do we do? We stick in a silent vowel ... Now the very velar nn starts affecting the vowel and drags it towards a more velar vowel - and at the same time the length shifts from the nn to the vowel (simply because it is much easier to say a long vowel as opposed to a long consonant)
ceann [kʲaːN]	Now, this is how you still pronounce this word in Irish and places like Kintyre and Argyll. In most other places though the long vowel has changed into a diphthong ...
ceann [kʲauN]	Look and sound familiar?

So that is what this broad and slender business is really about - it's a way of telling you whether a sound has been dragged back in your mouth (=broad =velar) or forward (=slender =palatal). And the "silent" letters are there to make life easier for you.

Footnotes? You betcha.

First, Scottish Gaelic has lost some sounds - there used to be a slender [b̊ʲ] [pʲ] [mʲ] [fʲ], but that distinction has been lost and replaced by a [j] glide. What's the difference? The difference is that [b̊ʲ] for example is one sound, made in one smooth motion in your mouth. What we get in modern Gaelic though is [b̊jɔː] beò - which is three sounds, a [b̊], [j] and an [ɔː].

Irish still has that distinction so you get pairs like bí [bʲiː] and buí [biː] where you can only tell the difference between 'to be' and 'yellow' by looking at the b.

What else? Want to know why the gentive palatalises in Gaelic (in a lot of cases anyway)? Going way back, there used to be simple endings which got stuck on the back of words to show case (things like nominative and gentive). In the case of masculine nouns, the nominative ending used to be -os, the genitive ending -i. See it already? If the -os in [kenːos] is the reason why the -nn in modern ceann is broad, then the -i in [kenːi] must be the reason why we have cinn today. Sure enough, we get [kenːi] > [kʲeɲːi] > [kʲiːɲ] - here the -i has dragged the [e] upward rather than downward (as we had with [e] and -os).

Sin agaibh e!