At different times philosophers have expressed their concern with the nature of judgement in different terms: the investigation may be called the theory of content, of belief, of propositions, of representation, of sense, etc. depending on which aspect of the matter is taken to predominate. The central problem is that of understanding the capacity of the mind to form, entertain, and affirm judgements, which are not simply strings of words but items intrinsically representing some state of affairs, or way that the world is or may be. The affirmation of a judgement is thus the making of a true or false claim. This capacity has been approached by thinking of the mind as stocked with ideas, or as capable of apprehending universals, or as stocked with inner representations, or by seeing the capacity as essentially linguistic in nature, or as arising from problem-solving behaviour that we share with animals (see animal thought), but no extensive consensus on the matter exists.