Similar tendencies, in a certain degree, affect the combinations _enp_, _enb_. They are liable to become _emp_, or _emb_. Any one may see that the word _enperor_ embarrasses the utterance. s. 227. The combination _tupt_ is stable, so also is the combination _tuft_. But the combination _tupth_ is unstable: since the _p_ is lene, the _th_ is a (so-called) aspirate. Hence arises a process of accommodation by which the word becomes either _tupt_ or _tufth_ (_tufth_). In respect to the unstable combination _tupth_, we may observe this, _viz._ that the ways of altering it are two. Either the first letter may be accommodated to the second, _tufth_, or the second may be accommodated to the first, _tupt_. Which of these two changes shall take place is determined by the particular habit of the language. In Greek we add to the radical syllable [Greek: tup]-, the inflectional syllable -[Greek: then]. The _first_ letter, [pi], is accommodated to the second, [theta], and the word becomes [Greek: tuphthen] (_tyfthaen_), as in [Greek: etuphthen] (_etyfthaen_). In English we add to the radical syllable _stag_, the inflectional syllable _s_. Here the _second_ letter is accommodated to the first, and the resulting word is not _staks_, but _stagz_. s. 228. The Irish Gaelic, above most other languages, illustrates a euphonic principle that modifies the vowels of a word. The vowels _a_, _o_, _u_, are full, whilst _i_, _e_, _y_, are small. Now if to a syllable containing a small vowel, as _buil_, there be added {159} a syllable containing a broad one, as _-am_, a change takes place. Either the first syllable is accommodated to the second, or the second to the first; so that the vowels respectively contained in them are either both full or both small. Hence arises, in respect to the word quoted, either the form _bu_a_l_a_m_, or else the form _bu_i_l_i_m_. s. 229. In the words _give_ and _gave_ we have a change of tense expressed by a change of vowel. In the words _price_ and _prize_ a change of meaning is expressed by a change of consonant. In _clothe_ and _clad_ there is a change both of a vowel and of a consonant. In the words _to use_ and _a use_ there is a similar change, although it is not expressed by the spelling. To the ear the verb _to use_ ends in _z_, although not to the eye. The following are instances of the permutation of letters. _Permutation of Vowels._