The study of the most general and abstract features of the world and categories with which we think: mind, matter, reason, proof, truth, etc. In philosophy, the concepts with which we approach the world themselves become the topic of enquiry. A philosophy of a discipline such as history, physics, or law seeks not so much to solve historical, physical, or legal questions, as to study the concepts that structure such thinking, and to lay bare their foundations and presuppositions. In this sense philosophy is what happens when a practice becomes self-conscious. The borderline between such ‘second-order’ reflection, and ways of practising the first-order discipline itself, is not always clear: philosophical problems may be tamed by the advance of a discipline, and the conduct of a discipline may be swayed by philosophical reflection (see also owl of Minerva). At different times there has been more or less optimism about the possibility of a pure or ‘first’ philosophy, taking an a priori standpoint from which other intellectual practices can be impartially assessed and subjected to logical evaluation and correction (see methodology). The contemporary spirit of the subject is hostile to any such possibility, and prefers to see philosophical reflection as continuous with the best practice of any field of intellectual enquiry. For the philosophy of various disciplines, see the titles of those disciplines.