What we have been saying about general principles applies to all types of informative writing, but there are specific writing tasks which we want to discuss as special cases, requiring their own special skills. Two types of writing with specialized aims, and therefore specialized tactics, are instructions and descriptions, which are the subjects of this and the next chapter.
Much writing is difficult to use because it fails to make clear decisions about what its aim is. This extract is from a document that was intended as an instruction:
The computer and the external equipment are placed in operation by procedures which incorporate loading magnetic tape, making certain manual selections, and starting the program. The operator first makes sure that all the equipment which is to be used by the program in store is properly prepared: that is to say that there is paper in the typewriter, that its margins are correctly adjusted, that its switch is set to COMPUTER, and that the power is on. If magnetic tape is to be used, the door of the tape handler is opened.
Difficulty is not caused by unreadable style. It is caused by the writer's confusion between the task of describing the process, and that of telling the reader how to operate the equipment.
Writers must be clear about the differences between these two modes of writing. Instructions enable the reader to do something with minimum hesitation. They do not necessarily require him or her to understand the operation; indeed to try to make the reader understand as well may interfere with the sequence of operations. A description, we shall argue in the next chapter, progresses from external overviews, through descriptions of the function and purpose, into detailed discussion of the compo-