Modus operandi (plural modi operandi) is a Latin phrase, approximately translated as "method of operation". The term is used to describe someone's habits of working, particularly in the context of business or criminal investigations. In English, it is often shortened to M.O.
The expression is often used in police work when discussing a crime and addressing the methods employed by the perpetrators. It is also used in criminal profiling, where it can help in finding clues to the offender's psychology. It largely consists of examining the actions used by the individual(s) to execute the crime, prevent its detection and/or facilitate escape. A suspect's modus operandi can assist in their identification, apprehension, or repression, and can also be used to determine links between crimes.
In business, modus operandi is used to describe a firm's preferred means of doing business and interacting with other firms.
The plural is modi operandi. The word operandi is a gerundium in the genitive case, "of operating"; gerundia can never be pluralised in Latin, as opposed to gerundiva. When a noun with an attribute in the genitive is pluralised, only the head noun normally changes, just as in English with of: a fact of life, two facts if life.
- Douglas, J. E. and A. W. Burgess, A. G. Burgess, R. K. Ressler. Crime classification manual (John Wiley & Sons, 2006) ISBN 0-7879-8501-5, p. 19-21.
- Vronsky, R. Serial Killers (Berkley Books, 2004) ISBN 0-425-19640-2, p. 412.
- Hazelwood, R. R, A. W. Burgess, Practical Aspects of Rape Investigation, (CRC Press, 2001) ISBN 0-8493-0076-2, p. 517.
- Berg, B.L. Criminal Investigation (McGraw-Hill, 2008) ISBN 978-0-07-340124-9
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