A study of how we reason correctly. It is a formal system of argument concerned with the structure of statements and arguments rather than their contents. Aristotle was the first to present a systematic account of logic. He explains the notion of terms such as inference and proposition and outlines valid forms of argument. The logic of Aristotle was interpreted and arranged by medieval thinkers and formal logic became important in philosophy. In the early 18th century, Leibniz suggested that logic could be elaborated into a universal problem-solving device based on the mathematical model. Difference of opinion could be settled not by debate but by calculation. His work inspired Boole and Frege, who in turn inspired both Russell and Wittgenstein to develop elaborate modern logical systems. Kant regarded the principles of logic as part of the framework of human understanding (built in to the human mind, not an externally developed set of rules). It is worthwhile to remember that even logicians recognise that logic as a form of reasoning can never lead to new discoveries. However, as a method of putting our findings into systematic order, it is a vital adjunct to enquiry.