Research abstracts are an increasingly important aspect of research articles in all knowledge fields, summarizing the full article and encouraging readers to access it. Graetz suggests that four main features contribute to this purpose--the use of past tense, third person, passive, and the non-use of negatives, although this claim has never been confirmed. In this article, we set out to explore the extent to which these forms are used in the abstracts of four disciplines, the functions they perform and how their frequency has changed over the past 30 years. Drawing on a corpus of 6,000 abstracts taken from the top 10 journals in each of four disciplines at three distinct time periods, we found high but decreasing frequencies of past tense and passives, an increasing number of third person forms, and more than one negation every two texts. We also noted a remarkable decrease of past tense and passives in the hard sciences and an increase in applied linguistics, with sociologists making greater use of negation. These results suggest that abstracts have developed a distinctive argumentative style, rhetorically linked both to their communicative function and to the changing social contexts in which academic writing is produced and consumed.