Front and back
From an articulatory perspective, phonemes can be described as front or back. Front vowels refer to vowels articulated towards the front of the mouth. This can either narrowly refer only to vowels articulated as far forward as possible in the mouth without creating a constriction that would be classified as a consonant, in which case it is opposed to near-front; or, more broadly, it can include both completely front and near-front vowels. A similar distinction holds for back vowels, which can be defined narrowly, or more broadly in a way that includes near-back vowels. However, acoustically there is little difference between a central vowel and a back vowel, with the result that the two are frequently grouped together into an even broader category of "back vowels", or a category of "non-front vowels".
A back consonant includes all consonants whose place of articulation is in the soft palate (velum) or farther back, including velar, uvular, pharyngeal, epiglottal, and glottal consonants. From the perspective of primary places of articulation, this includes all of the radical consonants and laryngeal consonants, and some of the dorsal consonants (specifically, excluding palatal consonants).
Front and back vowels are also known as acute and grave vowels, respectively. For consonants, however, front/back are not synonyms of acute/grave. Grave consonants include both back consonants and labial consonants, while acute consonants include all of front consonants except labial consonants. This suggests that a three-way division between labial, acute and back (vaguely speaking, "P-like", "T-like" and "K-like", respectively) might be useful in some contexts.
- Jacobson, Roman; On Language. Harvard University Press, 1990 p. 260