Labiodental

For labiodental fricatives [f v], air passes between the upper teeth and lower lip. Labiodental articulations are made with the upper teeth on either the outside or the inside of the lower lip. The two do not sound very different from each other and, as far as is known, no variety of English exploits the difference.

Because they are made without involvement of the tongue, labiodental fricatives are highly susceptible to secondary articulations made by different tongue postures: for example, compare the sounds at the beginning of ‘feast’ and ‘fool’, and you will probably hear an [i]-like secondary articulation in ‘feast’ – with the tongue close and front in the mouth,  – but an [u]-like one in ‘fool’, with the tongue body raised towards the velum, and perhaps with some lip-rounding . Retroflexion can also co-occur with labiodental articulation, and is common in productions of the word ‘from’, where there is often a period of friction and rhoticity simultaneously: .