Tacit knowledge (as opposed to formal or explicit knowledge) was first introduced into philosophy by Michael Polanyi in 1958. Tacit knowledge is defined as work related practical knowledge. It is that which is neither expressed nor declared openly but rather implied or simply understood and is often associated with intuition . This kind of knowledge is difficult to transfer to another person by means of writing it down or verbalising it. For example, stating to someone that London is in the United Kingdom is a piece of explicit knowledge that can be written down, transmitted, and understood by a recipient. However, the ability to speak a language, use algebra, or design and use complex equipment requires all sorts of knowledge that is not always known explicitly, even by expert practitioners, and which is difficult to explicitly transfer to users.