 In this connection, in the Logic of Scientific Discovery Popper introduces the technical concept of a “basic statement” or “basic proposition”, which he defines as a statement which can serve as a premise in an empirical falsification and which takes the singular existential form “There is an X at Y”. Basic statements are important because they can formally contradict universal statements, and accordingly play the role of potential falsifiers. To take an example, the (putative) basic statement “In space-time region k there is an apparatus which is a perpetual motion machine” contradicts the law of the conservation of energy, and would, if true, falsify it (2002: 48). Accordingly, Popper holds that basic statements are objective and are governed by two requirements: (a) the formal, that they must be both singular and existential and (b) the material, that they must be intersubjectively testable.