rendition of a spoken language. They have complex grammars of their own and can be used to discuss any topic, from the simple and concrete to the lofty and abstract. Sign languages are not inventions of educators, or ciphers of the spoken language of the surrounding community. Sign languages, like spoken languages, organize elementary, meaningless units into meaningful semantic units. This type of organization in natural language is often called duality of patterning. As in spoken languages, these meaningless units are represented as (combinations of) features, although coarser descriptions are often also made in terms of five "parameters": handshape (or handform), orientation, location (or place of articulation), movement, and non-manual expression. (These meaningless units in sign languages were initially called cheremes, from the Greek word for hand, by analogy to the phonemes, from Greek for voice, of spoken languages. Now they are sometimes called phonemes when describing sign languages too, since the function is the same, but more commonly discussed in terms of "features" or "parameters".) More generally, both sign and spoken languages share the characteristics that linguists have found in all natural human languages, such as transitoriness, semanticity, arbitrariness, productivity, and cultural transmission. Common linguistic features of many sign languages are the occurrence of classifier constructions, a high degree of inflection by means of changes of movement, and a topic-comment syntax. More than spoken languages, sign languages can convey meaning by simultaneous means, e.g. by the use of space, two manual articulators, and the signer's face and body. Though there is still much discussion on the topic of iconicity in sign languages, classifiers are generally considered to be highly iconic, as these complex constructions "function as predicates that may express any or all of the following: motion, position, stative-descriptive, or handling information". It needs to be noted that the term classifier is not used by everyone working on these constructions. Across the field of sign language linguistics the same constructions are also referred with other terms such as depictive signs. Today, linguists study sign languages as true languages, part of the field of linguistics. However, the category "sign languages" was not added to the Linguistic Bibliography/Bibliographie Linguistique until the 1988 volume, when it appeared with 39 entries. Relationships with spoken languages There is a common misconception that sign languages are somehow dependent on spoken languages: that they are spoken language expressed in signs, or that they were invented by