Two types of brackets are commonly used to enclose transcriptions in the IPA:
[Square brackets] indicate the phonetic details of the pronunciation, regardless of whether they are actually meaningful to a native speaker. This is what a foreigner who does not know the structure of a language might hear. For instance, the English word lulls is pronounced [ˈlɐɫz], with different el sounds at the beginning and end. This may be obvious to speakers of other languages, though a native English speaker might not believe it. Likewise, Spanish la bomba has two different b sounds to foreign ears, [laˈβomba], though a Spaniard might not be able to hear it. Omitting such detail does not make any difference to the identity of the word.
/Slashes/ indicate meaningful sounds called phonemes. Changing the symbols between slashes would either change the identity of the word or produce nonsense. Since there is no meaningful difference between the two el sounds in the word lulls, they need to be transcribed with the same symbol: /ˈlʌlz/. Similarly, Spanish la bomba is transcribed phonemically with a single b sound, /laˈbomba/. Thus a reader who is not familiar with the language in question might not know how to interpret these transcriptions.
A third kind of bracket is occasionally seen:
Either //double slashes// or |pipes| (or occasionally other conventions) show that the enclosed sounds are theoretical constructs that aren't actually heard. (This is part of morphophonology.) For instance, most phonologists argue that that the -s at the ends of verbs, which surfaces as either /s/ in talks /tɔːks/ or as /z/ in lulls /lʌlz/, has a single underlying form. If they decide this form is an s, they would write it //s// (or |s|) to claim that phonemic /tɔːks/ and /lʌlz/ are essentially //tɔːks// and //lʌls// underneath. If they were to decide it was essentially the latter, //z//, they would transcribe these words //tɔːkz// and //lʌlz//.
Lastly,
‹Angle brackets› may be used to represent the orthographic representation: ‹lulls›, ‹la bomba› (technically ⟨lulls⟩, ⟨la bomba⟩, but this is not universally supported). Because they're easier to type, the less-than and greater-than signs (< >) that appear on most keyboards are commonly used for this purpose.[1]
