In articulatory phonetics, a consonant is a speech sound that is articulated with complete or partial closure of the vocal tract. Examples are [p] and [b], pronounced with the lips; [t] and [d], pronounced with the front of the tongue; [k] and [g], pronounced with the back of the tongue; [h], pronounced in the throat; [f], [v], and [s], pronounced by forcing air through a narrow channel (fricatives); and [m] and [n], which have air flowing through the nose (nasals). Contrasting with consonants are vowels.
Since the number of speech sounds in the world's languages is much greater than the number of letters in any one alphabet, linguists have devised systems such as the International Phonetic Alphabet (IPA) to assign a unique and unambiguous symbol to each attested consonant. The English alphabet has fewer consonant letters than the English language has consonant sounds, so digraphs like , , , and are used to extend the alphabet, though some letters and digraphs represent more than one consonant. For example, the sound spelled in "this" is a different consonant from the sound in "thin". (In the IPA, these are [ð] and [θ], respectively.)
The word consonant comes from Latin oblique stem cōnsonant-, from cōnsonāns 'sounding-together', a calque of Greek σύμφωνον sýmphōnon (plural sýmphōna, σύμφωνα).
Dionysius Thrax calls consonants sýmphōna (σύμφωνα 'sounded with') because in Greek they can only be pronounced with a vowel. He divides them into two subcategories: hēmíphōna (ἡμίφωνα 'half-sounded'), which are the continuants, and áphōna (ἄφωνος 'unsounded'), which correspond to plosives.
This description does not apply to some languages, such as the Salishan languages, in which plosives may occur without vowels (see Nuxalk), and the modern concept of 'consonant' does not require co-occurrence with a vowel.
The word consonant may be used ambiguously for both speech sounds and the letters of the alphabet used to write them. In English, these letters are B, C, D, F, G, J, K, L, M, N, P, Q, S, T, V, X, Z and often H, R, W, Y.
