Phoneme, Phone and Allophone:

 In linguistics, the theory used to describe a language's distinctive sounds and their relations to one another is labeled the phoneme theory. In order to investigate, analyze, and interpret the various aspects and behaviors of speech sounds, there are three basic terms used in phonetics and phonology, and they are phoneme, phone, and allophone.

Phoneme:

A phoneme is the smallest unit of sound in a language that can change the meaning of a word. It is an abstract mental representation of a sound.  For example, in English, the words ‘pen’ and ‘ten’ differ only in their initial sounds: ‘pen’ beginning with /p/, and ‘ten’ with /t/. Therefore, /p/ and /t/ are two different phonemes. Notably, phonemes are written between slashes: /p/, /b/, /t/, etc.

Phone:

‘Phone’ is an actual spoken sound – the physical production of a sound. It is a phonetic unit used to indicate the smallest perceptible discrete segment of speech sounds.  Phones are concrete and can be recorded or heard.  For example, in English, spin and pin are both phones. Phones are written in square brackets: [p], [b], [t], etc.

Allophone:

Allophones are predictable variants of a phoneme that occur in different contexts without changing the meaning. There are different ways of pronouncing the same phoneme depending on the phonetic environment, like aspirated, unaspirated, and restricted I words’ initial, medial, and final positions. For example, the /p/ in pin [phIn] (aspirated) and in spin [spIn] (unaspirated) are allophones of the phoneme/p/.

Aspirated sound:

Aspiration refers to the puff of air released while producing a consonant sound. Usually, aspirated sounds are indicated with [h], this symbol. For example, pay/phei, tea [thI:], cholera [kholǝrǝ]. In English, stop consonants/p/,/t/, and/k/ possess the quality of aspiration. Usually, an English consonant before a stressed vowel is aspirated.

Summary table:

Term	Nature	Written As	Example
phoneme	abstract	/  /	/p/, /b/
phone	concrete	[ ]	Ph in pin, [p] in spin
Allophone	Variants of a phoneme	[  ]	[ph] and [p] are allophone of /p/