The central focus of Theoretical Computational Linguistics (TCL) is, on first approach, human language from the point of view of its computability. While the computer is the incarnation par excellence of an efficient computation model, the concerns of this subdiscipline of Linguistics and the questions it is most interested in addressing go beyond the bounds of a "Linguistics for computers".

A computation process is, in this context, understood to denote a procedure whereby, starting with a finite quantity of discrete objects, it is possible by applying a predetermined set of rules to arrive at a likewise finite, discrete object. Comprehending a sentence, for example, evidently involves a computation process in this sense. Based on the findings and methods of Logic TCL examines the characteristics (features) of such computation procedures in as far as they can be used to provide an insight into the structure of natural languages. Thus, for example in the fields of Logic and Theoretical Computer Science a refined hierarchy of computation processes has been devised which classifies these processes according to their increasing capacity. Against this background it becomes a question of high theoretical and practical interest at what level exactly in this hierarchy of computable processes the natural languages "per se" rank, as well as languages modelled on them with the aid of various linguistic theories. Should it turn out that we can only design our most important medium of communication by having recourse to abstract computing systems which lie beyond the practical computing capacity not only of presently available computers but also of those expected to become available in future, this circumstance would profoundly call into question the aims of linguistic research.

The results of studies on the complexity of natural language, besides their practical relevance as defined by means of theoretical reflections on the computability of such language, are also closely connected with the basic concepts of the essence of language established over the past four decades under the influence of the definitions generated by cognitive science. The object of cognitive science is the study of the mechanisms of perception and knowledge guided behaviour in humans, animals and machines. Cognitive science integrates results and methods of cognitive psychology, artificial intelligence, linguistics, philosophy, neurosciences and cognitive anthropology into its research programme. The underlying assumption is that any answers to problems that fall within the bounds of this discipline must obey the restriction that cognition be understood in the final analysis as a computation of (mental) representations. Human language, according to the precepts of cognitive science, belongs to the mental capabilities understood to function as a computation of such finite, discrete mental representations. Thus, if the methods thought to operate in morphology, syntax, semantics and pragmatics are so extremely complex that they not only exceed the practical computating capacity of putative computers but moreover even fail to fit into the framework of the abstract definition of a general computation process described above, then this would place hurdles in the way of computer linguistics and its proposed usage and, furthermore, one of the competing paradigms guiding the way homo sapiens sees himself would be rocked to the foundations. These involvements make it clear that, while theoretical computational linguistics, in spite of the implications of its name, does not aim most notably to reduce human language to the level of a computer programme, its study area - the analysis of language from the point of view of computation theory - has at the same time direct significance for the practical concerns of computational linguistics and for our own image of ourselves as speaking beings.