Deafness, most simply defined as an inability to hear. This definition, however, gives no real impression of how deafness affects function in society for the hearing-impaired person. The condition affects all age groups, and its consequences range from minor to severe. Profoundly deaf people have a hearing loss so severe that they cannot benefit from mechanical amplification, whereas hard-of-hearing people often can benefit, to varying degrees, from the use of such amplification.


Four types of hearing loss may be described. The first, conductive hearing loss, is caused by diseases or obstruction in the outer or middle ear and is not usually severe. Causes of conductive deafness include wax in the ears; infection of the external ear canal; perforated eardrum; glue ear with the loss of free movement of the ossicles (three small bones in the middle ear); otitis media (inflammation of the middle ear); a blockage in the Eustachian tube; and otosclerosis (hereditary form of deafness caused by bone growing into the space separating the middle and inner ear). A person with a conductive hearing loss can generally be helped by a hearing aid. Often conductive hearing losses can also be corrected through surgical or medical treatment. The second kind of deafness, sensorineural hearing loss or nerve deafness, results from damage to the sensory hair cells or the nerves of the inner ear and can range in severity from mild to profound deafness. Such loss occurs at certain sound frequencies more than others, resulting in distorted sound perceptions even when the sound level is amplified. Causes of sensorineural deafness include noise damage (acoustic trauma); ageing; Ménière’s disease; aminoglycoside antibiotics; certain diuretic drugs; aspirin; anti-malarial drugs; and acoustic nerve tumour. The third kind, mixed hearing loss, is caused by problems in both the outer or middle ear and the inner ear. Finally, central hearing loss is the result of damage to or impairment of the nerves of the central nervous system.

Deafness, in general, can be caused by illness or accident, or it may be inherited. Continuous or frequent exposure to sound levels above 85 decibels (dB), such as that produced by loud rock music (where dB can exceed 100 dB), can cause a progressive and eventually severe sensorineural hearing loss. A hearing aid may not help a person with a sensorineural loss.


Until the Middle Ages, most people believed that deaf people were incapable of learning language or of being educated in any way. By the 16th century, however, a few philosophers and educators began to reconsider the condition of deaf people. A Spanish Benedictine monk, Pedro de Ponce, is considered the first teacher of deaf students, and, in 1620, Juan Paulo Bonet, another Spaniard, wrote the first book on educating deaf people. The book contained a manual alphabet similar to the one used today.

During the 18th century, schools were established for deaf children in France by Abbé Charles Michel de l’Épée and, in Germany, by the educator Samuel Heinicke. The conflict that exists to this day as to whether deaf children should be educated by oral (lip-reading and speech) or manual (signs and finger spelling) methods dates from this time. The Abbé de l’Épée was a manualist and Heinicke an oralist; each knew of and studied the other’s methods.

Unless provided early with special training, people profoundly deaf from birth are incapable of learning to speak. Deafness from birth causes severe sensory deprivation, which can seriously affect a person’s intellectual capacity or ability to learn. A child who sustains a hearing loss early in life may lack the language stimulation experienced by children who can hear. The critical period for neurological plasticity is up to age seven. Failure of acoustic sensory input during this period results in failure of formation of synaptic connections and, possibly, an irremediable situation for the child. A delay in learning language may cause a deaf child’s academic progress to be slower than that of hearing children. The academic lag tends to be cumulative, so that a deaf adolescent may be four or more academic years behind his or her hearing peers. Deaf children who receive early language stimulation through sign language, however, generally achieve academically alongside their hearing peers.


Increasingly, the philosophy of total communication is being followed in schools and classes for deaf children. This philosophy encourages the combined use of whatever communication methods are appropriate to the deaf child, including speech, lip-reading, signing, Cued Speech, finger spelling, art, electronic media, mime, gesture, and reading and writing. Finger spelling is a system in which hand shapes and positions correspond to the letters of the written alphabet so that fingerspelling can be called “writing in the air”. Sign language (SL) is a language based on gestures, lip and eyebrow movements, and grammatical rules. Most countries have their own sign language, each as different as the languages spoken by the hearing is, and many with different dialects. Probably the most widely used are American Sign Language (ASL), which has no grammatical similarities with the English language whatsoever and takes a lot of its vocabulary from Old French Sign Language. British Sign Language (BSL) is used in the United Kingdom, Indian Sign Language in India, New Zealand Sign Language (NZSL) in New Zealand, and so on (see Sign Language).

The signs in SL are word-like units with both concrete and abstract meanings. Signs are made by either one or both hands, which assume distinctive shapes and movements. Spatial relations, directions, and orientation of the hand movements, as well as facial expressions and body movement, make up the grammar of SL. A number of invented (that is, not native languages) manual communication systems use the sign vocabulary of SL in combination with other hand movements to approximate the syntax and grammar of Standard English (see Paget-Gorman Sign System). Cued Speech is a system in which eight hand movements indicate the pronunciation of every syllable being spoken. It is a speech-based method that supplements lip-reading. Oral communication is the term used by educators to denote the teaching of speech as an expressive skill to deaf children. It means that speech and lip-reading are the only means of communication used for the transmission of thoughts and ideas.


Increasing numbers of deaf students are pursuing post-secondary educational programmes at tertiary education establishments that have special provisions and programmes for deaf students.

Today deaf people are employed in almost every vocation, except those where the good hearing is an obvious requirement—for example, being a commercial pilot. Deaf people are doctors, lawyers, teachers, and members of the clergy, as well as secretaries, accountants, chemists, farmers, and labourers. Discrimination does exist, as it does for other minority groups, but employers are increasingly hiring deaf people and making adjustments for them, such as adding special telephone devices or providing secretary-interpreters or other aids that enable the deaf employee to function effectively in work.