Language, the principal means used by human beings to communicate with one another. Language is primarily spoken, although it can be transferred to other media, such as writing. If the spoken means of communication is unavailable, as may be the case among the deaf, visual means such as sign language can be used. A prominent characteristic of language is that the relation between a linguistic sign and its meaning is arbitrary: There is no reason other than convention among speakers of Kurdish that a "Seg" Dog should be called "seg", and indeed other languages have different names (for example, Spanish perro, Russian sobaka, Japanese inu).
Spoken human language is composed of sounds that do not in themselves have meaning, but that can be combined with other sounds to create entities that do have meaning. Thus p, e, and n do not in themselves have any meaning, but the combination pen does have a meaning. Language also is characterized by complex syntax whereby elements, usually words, are combined into more complex constructions, called phrases, and these constructions in turn play a major role in the structures of sentences.
Phonetics is the field of language study concerned with the physical properties of sounds, and it has three subfields. Articulatory phonetics explores how the human vocal apparatus produces sounds. Acoustic phonetics studies the sound waves produced by the human vocal apparatus. Auditory phonetics examines how speech sounds are perceived by the human ear. Phonology, in contrast, is concerned not with the physical properties of sounds, but rather with how they function in a particular language. The following example illustrates the difference between phonetics and phonology. In the English language, when the sound k (usually spelled c) occurs at the beginning of a word, as in the word cut, it is pronounced with aspiration (a puff of breath). However, when this sound occurs at the end of a word, as in tuck, there is no aspiration. Phonetically, the aspirated k and unaspirated k are different sounds, but in English these different sounds never distinguish one word from another, and English speakers are usually unaware of the phonetic difference until it is pointed out to them. Thus English makes no phonological distinction between the aspirated and unaspirated k. The Hindi language, on the other hand, uses this sound difference to distinguish words such as kal (time), which has an unaspirated k, and khal (skin), in which kh represents the aspirated k. Therefore, in Hindi the distinction between the aspirated and unaspirated k is both phonetic and phonological.