Is the airflow central or lateral?

This parameter is rather a minor one, since it distinguishes only one phoneme of English from all others. For almost all English consonants, the airflow through the oral cavity is central. Recall that fricatives, like [s] or [f ], are produced with close approximation of the active and passive articulators; however, if you produce any fricative, you will feel that your articulators are actually pushed together quite tightly at the sides of the oral cavity, with the actual close approximation, and hence the narrow gap for airflow, left in the middle. The same is true for all the approximants except one: if you produce rip and lip, and focus on the initial consonants, you will notice that while the outgoing air for /r/, as usual, moves along the centre of the mouth, for /l/ it moves down the sides. If you find this difficult to feel, try making the related voiceless fricative sound found in Welsh names spelled with, like Llewellyn; because this is a fricative and involves close approximation of the articulators, the airflow is easier to observe. Alternatively, try making an [l] ingressively, pulling the air into your mouth instead of breathing it out, and feel the cold air moving inwards along the sides of your tongue. In English, both the clear and the dark allophones of /l/, and only these, have lateral airflow, and are known as lateral approximants.

Since the only case where the central versus lateral difference is distinctive in English involves /r/ and /l/, these should consistently be described as central and lateral respectively. Although in a particularly thorough description, all other sounds (except nasals, which have no oral airflow at all) should be explicitly stated to be central, this definition will generally be understood rather than stated below, since the other English sounds do not contrast with lateral sounds of the same place and manner of articulation, meaning that confusion is highly unlikely.