posed by William Molyneux to John Locke in the 17th century: if a man born blind, and able to distinguish by touch between a cube and a globe, were made to see, could he now tell by sight which was the cube and which the globe, before he touched them? The problem raises fundamental issues in epistemology and the philosophy of mind, and was widely discussed after Locke included it in the second edition of his Essay Concerning Human Understanding. A similar problem was also addressed earlier in the 12th century by Ibn Tufail (Abubacer), in his philosophical novel, Hayy ibn Yaqdhan (Philosophus Autodidactus). His version of the problem, however, dealt mainly with colors rather than shapes. Modern science may now have the tools necessary to test this problem in controlled environments. The resolution of this problem is in some sense provided by the study of human subjects who gain vision after extended congenital blindness. In one such study, subjects were unable to immediately link objects known by touch to their visual appearance, and only gradually developed the ability to do so over a period of days or months. This indicates that this may no longer be an unsolved problem in philosophy. Münchhausen trilemma The Münchhausen trilemma, also called Agrippa's trilemma, purports that it is impossible to prove any certain truth even in fields such as logic and mathematics. According to this argument, the proof of any theory rests either on circular reasoning, infinite regress, or unproven axioms. Metaphysics Why there is something rather than nothing The question about why is there anything at all instead of nothing has been raised or commented on by philosophers including Gottfried Wilhelm Leibniz, Martin Heidegger − who called it the fundamental question of metaphysics − and Ludwig Wittgenstein. The question is general, rather than concerning the existence of anything specific such as the universe/s, the Big Bang, mathematical laws, physical laws, time, consciousness or God. Problem of universals The problem of universals refers to the question of whether properties exist, and if so, what they are. Properties are qualities or relations or names that two or more entities have in common. The various kinds of properties, such as qualities and relations, are referred to as universals. For instance, one can imagine three cup holders on a table that have in common the quality of being circular or exemplifying circularity, or bear the same