[Revised entry by Gert-Jan Lokhorst, Stefania Centrone, and Pierluigi Minari on January 30, 2026.
Changes to: Main text, Bibliography, notes.html]
In 1926, Mally presented the first formal system of deontic logic. His system had several consequences which Mally regarded as surprising but defensible. It also had a consequence (“A is obligatory if and only if A is the case”) which Menger (1939) and almost all later deontic logicians have regarded as unacceptable. We will not only describe Mally’s system but also discuss how it may be repaired….

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