Affordances have long been understood to be an important factor in determining what happens on online social platforms. Software has features that makes certain behaviour easier and other behaviour more difficult; through such subtle nudges, people are guided into using the software, and the platform, for certain purposes. But affordances do not exist in a vacuum; they were created by people, who in turn were influenced by various factors and forces. In this thesis, I appropriate Bogost and Montfort's platform studies framework to perform a platform study of Twitter and IRC, reconstructing various features and types of expression that may be found on these platforms to reveal the processes that are at work in fundamentally shaping what people do on them. I start the thesis by reconstructing the development of both platforms, historically analysing specific features in detail and identifying which factors figured into their development. This reveals how seemingly unrelated or unidentified forces have the power to shape platforms and by extension what people do on them. Continuing, I take a closer look at various popular genres of expression that can be found on Twitter and IRC, again identifying the underlying affordances and forces that make them successful. The central theme here is the relation between a platform and its affordances, and to what extent and how they in fact have the power to determine what genres of expression are possible and successful. Finally, I investigate the imaginaries people hold about these platforms; what they think Twitter and IRC can do for them, and how these attitudes shift over time. This provides a more abstract, high-level overview of what these platforms are suitable for (or are 'perceived' to be suitable for), allowing for general insights on how a platform develops itself as a space for particular kinds of expression; and how such images compare to the expressive reality that was found in previous chapters.
