Taxpayer is a sole proprietor. Business is a consultant/independent contractor in a particular field (*not* related to investment, income-producing properties, or finance).
Taxpayer attends a trade conference for practitioners in that field. Conference is typical stuff like panel discussions/workshops/etc. on new developments in the field, discussions of problems and solutions encountered by practitioners, critiques of work, how to better find clients/develop the business, etc. Attendance at the conference is not required to meet any minimum standard of practice in the field.
The conference fee would certainly seem to meet the "ordinary and necessary" test.
But what category is it most appropriate to list it under? Education? (or is that supposed to be for more formal courses of study)?