The Scots Vowel-Length Rule, also known as Aitken's Law after Professor A.J. Aitken who formulated it, describes how vowel length in Scots and Scottish English is conditioned by environment. (Phonetics in IPA.) The rule affects all vowels in Central dialects, while in peripheral dialects some vowels remain unaffected. Scots (or Lallans, meaning Lowlands), often Lowland Scots to distinguish it from the Gaelic of the Highlands, is used in Scotland, as well as parts of Northern Ireland and border areas of the Republic of Ireland, where it is known in official circles as Ulster Scots or Ullans but by... Diagram showing the geographical locations of selected languages and dialects of the British Isles. ... The International Phonetic Alphabet is a phonetic alphabet used by linguists to accurately and uniquely represent each of the wide variety of sounds (phones or phonemes) the human vocal apparatus can produce. ...

• [ə], [ɪ], [ʌ], [ɛ] and [a] are usually short.
• [e], [i], [o], [u] and [ø] are usually long:
  • in stressed syllables before [v], [ð], [z], [ʒ] and [r].
  • before another vowel and
  • before a morpheme boundary.
• [ɑ], [ɒ] and [ɔ] are usually long in most dialects.
• The diphthong [əi] usually occurs in short environments and [aɪ] in the long environments described above.