There are two major classes of sounds traditionally distinguished in any language - consonants and vowels. The opposition "vowels vs. consonants" is a linguistic universal. The distinction is based mainly on auditory effect. Consonants are known to have voice and noise combined, while vowels are sounds consisting of voice only. From the articulatory point of view the difference is due to the work of speech organs. In case of vowels no obstruction is made, so on the perception level their integral characteristic is tone, not noise. In case of consonants various obstructions are made. So consonants are characterized by a complete, partial or intermittent blockage of the air passage. The closure is formed in such a way that the air stream is blocked or hindered or otherwise gives rise to audible friction. As a result consonants are sounds which have noise as their indispensable characteristic.
Russian phoneticians classify consonants according to the following principles: i) degree of noise; ii) place of articulation; iii) manner of articulation; iv) position of the soft palate; v) force of articulation.
(I) There are few ways of seeing situation concerning the classification of English consonants. According to V.A. Vassilyev primary importance should be given to the type of obstruction and the manner of production noise. On this ground he distinguishes two large classes:
a) occlusive, in the production of which a complete obstruction is formed;
b) constrictive, in the production of which an incomplete obstruction is formed. Each of two classless is subdivided into noise consonants and sonorants.
Another point of view is shared by a group of Russian phoneticians. They suggest that the first and basic principle of classification should be the degree of noise. Such consideration leads to dividing English consonants into two general kinds: a) noise consonants; b) sonorants.
The term "degree of noise" belongs to auditory level of analysis. But there is an intrinsic connection between articulatory and auditory aspects of describing speech sounds. In this case the term of auditory aspect defines the characteristic more adequately.
Sonorants are sounds that differ greatly from other consonants. This is due to the fact that in their production the air passage between the two organs of speech is fairly wide, that is much wider than in the production of noise consonants. As a result, the auditory effect is tone, not noise. This peculiarity of articulation makes sonorants sound more like vowels than consonants. Acoustically sonorants are opposed to all other consonants because they are characterized by sharply defined formant structure and the total energy of most of them is very high.
There are no sonorants in the classifications suggested by British and American scholars. Daniel Jones and Henry A. Gleason, for example, give separate groups of nasals [m, n, η], the lateral  and semi-vowels, or glides [w, r, j (y)]. Bernard Bloch and George Trager besides nasals and lateral give trilled [r]. According to Russian phoneticians sonorants are considered to be consonants from articulatory, acoustic and phonological point of view.
(II) The place of articulation. This principle of consonant classification is rather universal. The only difference is that V.A. Vassilyev, G.P. Torsuev, O.I. Dikushina, A.C. Gimson give more detailed and precise enumerations of active organs of speech than H.A. Gleason, B. Bloch, G. Trager and others. There is, however, controversy about terming the active organs of speech. Thus, Russian phoneticians divide the tongue into the following parts: (1) front with the tip, (2) middle, and (3) back. Following L.V. Shcherba's terminology the front part of the tongue is subdivided into: (a) apical, (b) dorsal, (c) cacuminal and (d) retroflexed according to the position of the tip and the blade of the tongue in relation to the teeth ridge. А.С. Gimson's terms differ from those used by Russian phoneticians: apical is equivalent to forelingual; frontal is equivalent to mediolingual; dorsum is the whole upper area of the tongue. H.A. Gleason's terms in respect to the bulk of the tongue are: apex - the part of the tongue that lies at rest opposite the alveoli; front - the part of the tongue that lies at rest opposite the fore part of the palate; back, or dorsum - the part of the tongue that lies at rest opposite the velum or the back part of the palate.
(III) A.L. Trakhterov, G.P. Torsyev, V.A. Vassilyev and other Russian scholars consider the principle of classification according to the manner of articulation to be one of the most important and classify consonants very accurately, logically and thoroughly. They suggest a classification from the point of view of the closure. It may be: (1) complete closure, then occlusive (stop or plosive) consonants are produced; (2) incomplete closure, then constrictive consonants are produced; (3) the combination of the two closures, then occlusive- constrictive consonants, or affricates, are produced; (4) intermittent closure, then rolled, or trilled consonants are produced.
A.C. Gimson, H.A. Gleason, D. Jones and other foreign phoneticians include in the manner of noise production groups of lateral, nasals, and semivowels - subgroups of consonants which do not belong to a single class.
Russian phoneticians subdivide consonants into unicentral (pronounced with one focus) and bicentral (pronounced with two foci), according to the number of noise producing centers, or foci.
According to the shape of narrowing constrictive consonants and affricates
are subdivided into sounds with flat narrowing and round narrowing.
(IV) According to the position of the soft palate all consonants are subdivided into oral and nasal. When the soft palate is raised oral consonants are produced; when the soft palate is lowered nasal consonants are produced.
(V) According to the force of articulation consonants may be fortis and lenis. This characteristic is connected with the work of the vocal cords: voiceless consonants are strong and voiced are weak.