The aims when testing applications that use natural language (NL) as their interface style should not be of the form ``can I fool it?'', but rather of the ``can I use it?'' category. Since it is not yet feasible to build a purely natural language interface, it will always be possible to find examples of phrases that the system will not be able to deal with, and hence a tester will always be able to fool the system [24,8] and this information should always be kept in mind when dealing with NL systems.
The main measure of the ease of use of a system is its habitability, and it is effected by the conceptual, functional, syntactic and lexical domains.