Abstract
This study examines three dimensions of paragraph topic sentence use in a corpus of scientific writing made up of research articles in biochemistry, geology, psychology, and sociology: 1. frequency of topic sentence use; 2. variation of topic sentence frequency in five rhetorical divisions; 3. variation of topic sentence types in these rhetorical divisions. Although the scientific writers used topic sentences in 55 percent of their paragraphs, differences existed among rhetorical divisions as to topic sentence frequency: writers used topic sentences quite often in results, results/discussion, and discussion, but quite seldom in methodology. Furthermore, topic sentence types differed across the divisions. In methodology, the topic announcement predominated; in discussion and introduction, the propositional occurred most often; in results and results/discussion, there was a balance of the two types. All these variations are thought to be related to differences in function (reporting facts versus interpreting) and texture (attributive versus logical text) across the rhetorical divisions. These variations may also affect ways of teaching paragraph skills in scientific writing.