Different sorts of traditional symbols are used by humans to convey a particular meaning; for example, the cross represents Christianity for a large proportion of humanity. The alphabet can be used to build up different definitive meanings using various systematic rules. It is important in the construction of an artificial language that all the users agree on the rules that are to be applied to it. This is the case both in more complex languages (for example, those that resemble the natural ones) and in the simpler ones, such as those used by machines of different types or as explanations on VDU screens.
The assumptions necessary before a language can be built up are, first, that everyone agrees what the different characters mean, and secondly that there are certain predetermined semantics. There must also be a grammar, which specifies the way in which the different symbols can be combined. Finally, the symbols must be designed in such a way that they can be understood by other people. As far as visual symbols are concerned, they must be able to be clearly seen and understood in the situation in which they are designed for use.
Languages may be termed natural or artificial. Natural languages are often learned in childhood, or after very comprehensive training and/or education. More complex artificial languages that are to be used in a similar way to the natural languages also require a very comprehensive education and training. In the design of languages for use in different technical applications in industry, special stress must be laid on the need to make the rules simple so that as far as possible they are selfevident. Even if one can set out such very simple rules for the language, it is still necessary for the rules to be put down in writing so that everyone agrees on which rules are valid. In the following part of this section, we present semantics, then a grammar, and finally a number of viewpoints on the visual detectability of symbolic languages which can be used on VDU screens.