Master's degrees. These are sometimes placed in a further hierarchy, starting with degrees such as the Master of Arts (from Latin "Magister artium"; M.A.) and Master of Science (from Latin "Magister scientiæ"; M.Sc.) degrees, then the Master of Philosophy degree (from Latin "Magister philosophiæ"; M.Phil.), and finally the Master of Letters degree (from Latin "Magister litterarum"; M.Litt.) (all formerly known in France as DEA or DESS before 2005, and nowadays Masters too). In the UK, master's degrees may be taught or by research: taught master's degrees include the Master of Science and Master of Arts degrees which last one year and are worth 180 CATS credits (equivalent to 90 ECTS European credits), whereas the master's degrees by research include the Master of Research degree (M.Res.) which also lasts one year and is worth 180 CATS or 90 ECTS credits (the difference compared to the Master of Science and Master of Arts degrees being that the research is much more extensive) and the Master of Philosophy degree which lasts two years. In Scottish Universities, the Master of Philosophy degree tends to be by research or higher master's degree and the Master of Letters degree tends to be the taught or lower master's degree. In many fields such as clinical social work, or library science in North America, a master's is the terminal degree. Professional degrees such as the Master of Architecture degree (M.Arch.) can last to three and a half years to satisfy professional requirements to be an architect. Professional degrees such as the Master of Business Administration degree (M.B.A.) can last up to two years to satisfy the requirement to become a knowledgeable business leader.