Scientists represent their world, grouping and organizing phenomena into classes by means of concepts. Philosophers of science have historically been interested in the nature of these concepts, the criteria that inform their application and the nature of the kinds that the concepts individuate. They also have sought to understand whether and how different systems of classification are related and more recently, how investigative practices shape conceptual development and change. Our aim in this paper is to provide a critical overview of some of the key developments in this philosophical literature and identify some interesting issues it raises about the prospects of the so-called "special sciences", including psychiatry, psychology, and the mind-brain sciences more generally, to discover natural kinds. 2. Principles of classification: a brief historical overview 2.1. Conventionalism Human beings impose conceptual order on their world. In the most basic terms, we are born into a world of language users; learning the meanings of words requires the abilities to detect objects having certain properties in the world, to recognize similarities and differences among those objects with respect to those properties and to understand that things that others identify using the same name share certain properties in common. We learn these basic rules of classification and assign things that share properties in common to groups having unique names. Common examples of groups include stars, mammals, trees, beliefs and feelings. We learn that stars have the basic properties of being luminous and visible in the night sky and that beliefs are things that humans and some non-human animals have that can be assigned a truth value. Sometimes we place unlike things into the same group-we misclassify

Serotonergic (or “classic”) psychedelics have struck many researchers as raising significant philosophical questions that, until recently, were largely unexplored by academic philosophers. This paper provides an overview of four emerging lines of research at the intersection of academic philosophy and psychedelic science that have gained considerable traction in the last decade: selfless consciousness, psychedelic epistemology, psychedelic ethics, and spiritual/religious naturalism. In this paper, we highlight philosophical questions concerning (i) psychedelics, self-consciousness, and phenomenal consciousness, (ii) the epistemic profile of the psychedelic experience; (iii) ethical concerns about the appropriate use of psychedelics; and (iv) whether spiritual or religious dimensions of psychedelic use are compatible with a naturalistic worldview.