There is a general, though largely unexamined, assumption among those interested in such things that writing in many domains has become less formal in recent years (e.g. Adel, 2008;Foster, 2005;Fairclough, 2001) . Observers have noticed a gradual shift away from standard detached and impersonal styles of writing to ones that allow more personal comment, narration and stylistic variation, so that Mair, for example, notes "a trend towards the informal and the colloquial in written communication" (1998: 153) and Leedham (2015) found greater informality in undergraduate essays.This trend towards informality might be seen as part of a contemporary zeitgeist which blurs overt hierarchies and values interpersonal engagement or, alternatively, be regarded as another form of insidious persuasion, what Fairclough (2001: 52) calls "synthetic personalization". It is possible, however, that the informality which has invaded a large range of written and spoken domains once characterized by formality (journalism, business correspondence, administrative documents, etc.) has also spread to academic writing. Indeed, it has been fashionable among applied linguists in recent years to search for evidence of greater interactivity in academic prose and identify the ways that writers craft an inclusive relationship with their readers (e.g. Hyland, 2004).In this paper we explore this issue and investigate whether academic writing is becoming less formal and, if so, in what ways and in what disciplines. We first attempt to characterize the notion of 'informality' and how it is understood by academic discourse analysts and those who advise authors on academic style. Needless to say, while we know it when we see it, we find 'informality' to be a slippery concept, difficult to pin down with a clear definition. It is typically either defined in contrast with formality, or in terms of lists of language features which are thought to comprise 'informal elements', such as using imperatives, employing "I" or starting sentences with "but". Focusing on published research articles as the most important genre of academic writing, we then undertake a comparative study of three corpora composed of papers in four fields drawn from three distinct time periods, examining the frequencies of key 'informal elements'.
What is informality?The first place to start is with a definition or characterization of the term, but this is not altogether straightforward. Informality is generally hetero-defined, the Latin prefix meaning "not, opposite of, without" (Online Etymology Dictionary, 2010) and demarcated as the absence of formality. It therefore presupposes the existence of formality and a recognized set of practices built on a structure, authority or system. Thus the Cobuild dictionary defines formal speech as "very correct and serious rather than relaxed and friendly" while in pragmatics, formality is associated with 'negative politeness' and the use of distancing behaviour to respect the other's face and their wish not to be imposed on (Brown & Levinson, 1987)...