A Corpus Study of Negative Imperatives in Natural Language Instructions

A Corpus Study of Negative Imperatives in Natural Language Instructions* Keith Vander Linden t Information Technology Research Institute University of Brighton Brighton BN2 4AT, UK knvl@itri.brighton.ac.uk Barbara Di Eugenio Computational Linguistics Carnegie Mellon University Pittsburgh, PA, 15213 USA dieugeni@andrew.cmu.edu Abstract In this paper, we define the notion of a preventative expression and discuss a corpus study of such expressions in in- structional text. We discuss our cod- ing schema, which takes into account both form and function features, and present measures of inter-coder reliabil- ity for those features. We then discuss the correlations that exist between the function and the form features. 1 Introduction While interpreting instructions, an agent is con- tinually faced with a number of possible actions to execute, the majority of which are not appro- priate for the situation at hand. An instructor is therefore required not only to prescribe the ap- propriate actions to the reader, but also to pre- vent the reader from executing the inappropriate and potentially dangerous alternatives. The first task, which is commonly achieved by giving simple imperative commands and statements of purpose, has received considerable attention in both the interpretation (e.g., (Di Eugenio, 1993)) and the generation communities (e.g., (Vander Linden and Martin, 1995)). The second, achieved through the use of preventative expressions, has received corn siderably less attention. Such expressions can in- dicate actions that the agent should not perform, or manners of execution that the agent should not adopt. An agent may be told, for example, "Do not enter" or "Take care not to push too hard". * This work is partially supported by the Engi- neering and Physical Sciences Research Council (~n,- sac) Grant J19221 and by the Commission of the Eu- ropean Union Grant LRE-62009. t After September 1, Dr. Vander Linden's address will be Dept. of Mathematics and Computer Science, Calvin College, Grand l~apids, MI 49546, USA. Both of the examples just given involve negation ("do not" and "take care not"). Although this is not strictly necessary for preventative expressions (e.g., one might say "stay out" rather than "do not enter"), we will focus on the use of negative forms in this paper. We will use the following categorisation of explicit preventative expressions: • negative imperatives proper (termed DONT imperatives). These are characterised by the negative auxiliary do not or don't. (1) Your sheet vinyl floor may be vinyl as- bestos, which is no longer on the mar- ket. Don't sand it or tear it up because this will put dangerous asbestos fibers into the air. • other preventative imperatives (termed neg- TC imperatives). These include take care and be careful followed by a negative infiniti- val complement, as in the following examples: (2) To book the strip, fold the bottom third or more of the strip over the middle of the panel, pasted sides together, taking care not to crease the wallpaper sharply at the fold. (3) If your plans call for replacing the wood base molding with vinyl cove molding, be careful not to …

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