There is still a lot of confusion concerning the concept of deafness. Who are the deaf? How many are they? To have precise and official data is almost impossible, principally because only a doctor can determine the degree of deafness in a subject.

Deafness is a more or less heavy reduction of the auditory faculty. Many factors have to be taken into consideration, which are all closely connected to each other: how old was the person when the hearing reduction occurred, the actual decibels lost, and the re-educational linguistic method that has been adopted.
Regarding age, it is very important to understand whether the subject lost the hearing before (from 0 to 1 year), during (from 1 to 12 years) or after linguistic learning (after the age of 12 years), distinguishing a pre-, peri- and postlingual deafness.

From a clinical point of view, the taxonomy is based on the loss of hearing decibels:
mild deafness (from 20 to 40 dB); moderate deafness (from 40 to 70 dB); severe deafness (from 70 to 90 dB); profound deafness (from 90 dB onwards).

If in the first two cases the problems are of a moderate nature, great results can be obtained thanks to the use of hearing aids and good logopaedics. Instead in the last two cases the auditory perception is almost annulled and thus a long and complex logopaedics is needed. Erroneously one tends to consider the “deaf” as these last two categories only.

The linguistic method of education is of extreme importance. Principally two methods are distinguished:

› oralism: it is characterized by the rejection of any gestural form of communication, it aims to maximize the so called “auditory residuals” and it concentrates mainly on lip-reading, which is fundamentally helped by the extreme phonetic simplicity of same languages (italian, for example, but also spanish and german).

› manualism: it is mainly  based on the education of English Sign Language (ESL).

This distinction is also relevant from a sociocultural point of view in order to identify the deaf in their respective communities (hearing/non hearing). In English-speaking countries manualism is principally used, due to the poor correspondence between both written and oral English language. Anyhow, it should be always kept in consideration that for various reasons, the deaf generally do not reach a high level of schooling.