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Britannica Sources used in this answer

Why is the /p/ in “pin” aspirated but the /p/ in “spin” usually unaspirated?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Diagram of a human head in profile showing the location of vocal organs and possible places of articulation for speech sounds, with labels for lips, teeth, tongue, palate, uvula, pharynx, and vocal cords, and numbered regions corresponding to types of articulation such as bilabial, alveolar, and velar.
phonetics Diagram depicting the location of human vocal organs and possible places of articulation used for speech.

In English, the difference in the pronunciation of the /p/ sound in "pin" and "spin" is determined by phonological rules regarding the timing of the glottis.

Both words contain the same voiceless bilabial stop phoneme /p/, but they are realized as different allophones depending on their phonetic environment:

  • Aspiration in "pin": When a voiceless stop occurs at the beginning of a word, the glottis remains in a voiceless position for a short time after the release of the stop. This period of voicelessness during the release results in aspiration, characterized by a forceful expulsion of air.312
  • Unaspiration in "spin": When the voiceless stop occurs after a voiceless alveolar fricative (the /s/ sound), the voicing begins as soon as the lips come apart. Because there is no period of voicelessness following the release, the sound is unaspirated.312

These variations are predictable patterns in English phonetics rather than distinct phonemic differences.1