Educational researchers have concluded that there are threshold concepts in a large number of disciplines. Yet, these researchers have not paid enough attention to the objection to the theory. It is beset with severe definitional and empirical problems. I will portray definitions of 'threshold concepts' provided by Land and Meyer, the founding fathers of the threshold concept theory. I argue, in the first place, that the definitions fail and, in the second place, that even if the definitional problems were solved and we were able to identify some threshold concepts, their scientific importance would be limited if not nil.