would be otherwise, as when a and o are changed to ao before dh and gh. The number of instances in which consonants are absolutely silent, however, is by no means great. 'Silent' consonants are not always silent. They may be silent in one dialect and not in another. Indeed, apart from the cases in which there is immediate contact with a liquid or another consonant the instances of consonants that are silent in every dialect are comparatively few in number, and even where they are in contact with liquids or other consonants they are not without phonetic influence in the pronunciation of the word. Even th at the end of accented syllables in many instances is not silent in Arran, Kintyre, and Islay, or, though with a different pronunciation, in the west of Ross-shire.
Silent consonants owe not only their retention or introduction in many cases to their vowel neighbours. They often owe their silence to those same vowels. They have lost their sounds through aspiration, and aspiration has been caused by the vowels. Aspiration took place whenever a single consonant stood between two vowels in early Gaelic speech. No consonant, unless supported by its own double or by some other consonant, was strong enough to resist the force of vowels on either side of it, and remain unchanged in such a position. In the case, for example, of those consonants called mutes or stops, b, p, c, g, d, t, the organs of utterance which should be closed completely so as to stop or intercept the emission of breath between the two vowels, were only partially closed in anticipation of the coming vowel, and so permitted an emission of breath or aspiration that in place of the 'stops' caused the sounds that were really uttered to be the corresponding 'aspirates' or aspirated consonants. The consonants that were themselves spirants, as v and s, when they came into such a position, vanished altogether. The liquids in such positions also underwent a change, and though it is not properly aspiration, though often conveniently included under that distinctive designation, it agrees with aspiration in that it takes place in the same circumstances and arises from the same cause. The great cause of many,