Considered as a modality, speech is very different from other modalities like written language or graphics.

The list below is just a brief list of some properties that are important to remember when designing dialogue. A comprehensive account of modality theory can be found in [Bernsen 2002, Bernsen 1999].

Speech feature Description Opposes
Serial No parallel information. Graphics
Temporal Speech takes time and puts demands on the users memory. Graphics
Volatile Disappears as fast as it is presented. Graphics
Open No finite set of symbols. Keyboard
Referential Speech (language) can refer to non-visible objects. Graphics