Inner speech is a mental phenomenon that is normally described as the inner voice in our heads, talking to ourselves in silence or thinking in words. It is a pervasive phenomenon, as it takes place around 25 per cent of our waking time and it has been traditionally tied to our conception of the experience of thinking. Despite the multiple references to the phenomenon, inner speech remained quite a marginal topic of inquiry both in philosophy and psychology, but this tendency has started to change recently. This shift of focus is certainly not without reason, given both the wide range of questions that arise regarding the properties and functions of inner speech itself and the connections that inner speech has with other relevant mental phenomena such as language, thought, consciousness, perception and action. Indeed, inner speech is an introspectively salient and empirically tractable conscious phenomenon that raises various interesting philosophical puzzles, being it intrinsically linguistic in nature, but also presenting sensory, semantic, phonological-auditory and motoric aspects.

The aim of INACT is to take inner speech as the main focus of philosophical inquiry within an interdisciplinary framework that integrates results from phenomenology, psychology, and psychiatry. The main objective is to develop a view of inner speech as independent from although related to thinking and to be able to map different inner speech profiles as they present in different mental conditions.

An integral, conceptually consistent and empirically plausible account of inner speech as a linguistic activity will benefit from a theoretical and empirically informed exploration of inner speech in schizophrenia (specially the phenomena of auditory verbal hallucinations and inserted thoughts) and autism, and its relation to affordance experiences.