Affection (linguistics)

Affection, in the linguistics of the Celtic languages, is the change in the quality of a vowel under the influence of the vowel of the following final syllable. It is a type of assimilation, or, more specifically, anticipatory assimilation at a distance.
The two main types of affection are a-affection and i-affection. There is also u-affection, which is more usually referred to as u-infection. I-affection is an example of i-mutation and may be compared to the Germanic umlaut, and a-affection is similar to Germanic a-mutation. More rarely, the term "affection", like "umlaut", may be applied to other languages and is then a synonym for i-mutation generally.
The vowel triggering the change was often later lost; for example, the plural of Welsh "bard, poet" is, from *bardī with i-affection. In other cases, the grammatical suffix that causes i-affection remains, such as in, plural of "patient ".