This study is concerned with an analysis of the research arising from three quite different perspectives on instructional text - the `physical characteristics' research (legibility, layout, and readability), the `improvement of text' research (visual illustrations, adjunct aids, and typographical cueing), and the `learning theories' research (representation of knowledge, human memory, and quality of learning). From this analysis there is synthesised principles for the design of instructional text against which heuristic practice in text design is evaluated and from which a nascent theory of instructional text design is evolved. The principles derived from the various research perspectives provide a basis for the manipulation of text design elements in order to ensure that (a) existing knowledge in the reader can be activated, and (b) new knowledge can be assimilated in a manner facilitative of comprehension by (i) presentation in a structured and organised way, and (ii) appropriately highlighted through verbal and typographic cueing supported, as required, by verbal illustration and organisation. The emerging theory of instructional text design suggests: a topical analysis to determine the heirarchic relationship of ideas within the topic and the desired learning outcomes or objectives; a consideration of the linguistic aspects of the text; a consideration of the role of visual illustrations; and a consideration of the physical parameters of the text. These activities are concerned, respectively, with the design areas of structure and organisation, readability, visual illustration, and legibility, and are summed up in the acronym SORVIL
