"I was taught, 55 years ago, an is used if the beginning letter is a vowel, vowel sound or an H." I'm not convinced this is currently accurate. I don't believe you automatically use "an" in front of...
Linguistics is the study of languages and covers all aspects of language, including phonetics (sounds humans make), phonology (the way sounds interact in a given language), semantics (meanings),...
Linguistics is the scientific study of languages and includes many theories to include other branches and disciplines of study such as psychology, sociology, anthropology,history,cognitive science...