Phonetics Students: square brackets for PHONETIC transcriptions. Forward slashes for PHONEMIC transcriptions - I heard you say. But ! Some authors do not adhere to this "rule" and this means you

have to specify whose system it is. So, Japanese [r] [l], English /r/ and /l/ .

But when discussing the QUALITY of a vowel (French) you are allowed to use brackets.

Allophones: brackets. Although I strongly disagree with tails wagging dogs in the case of papers written to prove a point.

This means: lecturers who see too many trees and not the wood in a totality are bound to pick on the odd bracket going slashy. As long as your ideas stand their ground (eg French vowels being unstable) you ought not to worry about these - remember the "so and so has written"/said necessity of an essay.