Phonetics and Phonology

Phonetics (from the Greek word phone = sound/voice) is a fundamental branch of Linguistics and itself has three different aspects:

• Articulatory Phonetics - describes how vowels and consonants are produced or “articulated” in various parts of the mouth and throat;
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Acoustic Phonetics - a study of how speech sounds are transmitted: when sound travels through the air from the speaker's mouth to the hearer's ear it does so in the form of vibrations in the air;
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Auditory Phonetics - a study of how speech sounds are perceived: looks at the way in which the hearer’s brain decodes the sound waves back into the vowels and consonants originally intended by the speaker.

phonology

phonology,  study of the sound patterns that occur within languages. Some linguists include phonetics, the study of the production and description of speech sounds, within the study of phonology.

Diachronic (historical) phonology examines and constructs theories about the changes and modifications in speech sounds and sound systems over a period of time. For example, it is concerned with the process by which the English words “sea” and “see,” once pronounced with different vowel sounds (as indicated by the spelling), have come to be pronounced alike today. Synchronic (descriptive) phonology investigates sounds at a single stage in the development of a language, to discover the sound patterns that can occur. For example, in English, nt and dm can appear within or at the end of words (“rent,” “admit”) but not at the beginning.

Linguistics

Linguistics is the scientific study of human language.^[1][2][3][4] Linguistics can be broadly broken into three categories or subfields: the study of language form, of language meaning, and of language in context.
The first is the study of language structure, or grammar. This focuses on the system of rules followed by the speakers (or hearers) of a language. It encompasses morphology (the formation and composition of words), syntax (the formation and composition of phrases and sentences from these words), and phonology (sound systems). Phonetics is a related branch of linguistics concerned with the actual properties of speech sounds, nonspeech sounds, and how they are produced and perceived.