 Techne is, at the most basic level, what can be learned and taught. The word is usually used for a body of professional knowledge, mastered by experts on whom laypeople may safely rely. It is often translated “art” or “craft” or “skill,” but in these pages it will be rendered “expert knowledge.” Navigation and medicine are frequent examples of expert knowledge. To establish your credentials in expert knowledge, you should be able to identify your teachers and students (Laches 185b), as well as the specific field of your expertise, which you must have mastered as a whole (e.g., Ion 532b, ff.). You should also, ideally, be able to give an account of the aim of your profession (e.g. physical health for medicine, Laches 190a, moral health for legislation, Gorgias 465a). Expert knowledge must be rational in its ability to account for what it does, and rationality in this context seems to consist in basing your decisions on definitions (logoi) that can withstand Socratic questioning. .