What is implicit bias?

Research programs in empirical psychology over the past few decades have led scholars to posit implicit biases. This is due to the development of innovative behavioural measures that have revealed aspects of our cognitions which may not be identified on self-report measures requiring individuals to reflect on and report their attitudes and beliefs. But what does it mean to characterise such biases as implicit? Can we satisfactorily articulate the grounds for identifying them as bias? And crucially, what sorts of cognitions are in fact being measured; what mental states or processes underpin such behavioural responses? In this paper, we outline some of the philosophical and empirical issues engaged when attempting to address these three questions. Our aim is to provide a constructive taxonomy of the issues, and how they interrelate. As we will see, any view about what implicit bias is may depend on a range of prior theoretical choices.