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Mutatis mutandis is a Latin phrase meaning "changing [only] those things which need to be changed" or more simply "[only] the necessary changes having been made".
The phrase carries the connotation that the reader should pay attention to differences between the current statement and a previous one, although they are analogous.[clarification needed] It can be understood as meaning "acknowledging the difference between the two" or (more succinctly) as "acknowledging differences." This term is used frequently in economics, philosophy, logic, and law, to parameterize a statement with a new term, or note the application of an implied, mutually understood set of changes. The phrase is also used in the study of counter-factuals, wherein the requisite change in the factual basis of the past is made and the resulting causalities are followed.
Both "mutatis" and "mutandis" come from the Latin verb "mūtō" (principal parts: mūtō, mūtāre, mūtāvī, mūtātum), meaning "to change."
Mūtātīs is the perfect passive participle (ablative plural neuter), literally "having been changed."
Mūtandīs is the gerundive (ablative plural neuter), which can convey the idea of necessity, hence: "things needing to be changed".
The phrase is an ablative absolute construction.
Plain English 
In the wake of the Plain English movements, some countries attempt to replace the Latin phrases existing in their legislatures with the English phrases. "Mutatis mutandis" may be replaced by "with the necessary modifications" as being used in the English translation of the German Civil Code by the German Ministry of Justice. For example:
"Section 27 (Appointment of and management by the board). ...(3) The management by the board is governed by the provisions on mandate in sections 664 to 670 with the necessary modifications."
- "A friend of mine has a son whose case, mutatis mutandis, is very much like yours" - Proust, Within a Budding Grove.
- 1998, U.S. bankruptcy court analysis of use in a legal document:
This Latin phrase simply means that the necessary changes in details, such as names and places, will be made but everything else will remain the same.
- "We can in fact only define a weed, mutatis mutandis, in terms of the well-known definition of dirt — as matter out of place. What we call a weed is in fact merely a plant growing where we do not want it." — E.J. Salisbury, The Living Garden, 1935.
- "The proof that Q is universal relative to the set of all 3-bit gates applies step by step, mutatis mutandis, to Q4." — D. Deutsch, Quantum computational networks, Proc. R. Soc. Lond. A 425, pp. 85, 1989.
- "Mutatis mutandis. He did what needed to be done." - Companion of Trevor Goodchild, Aeon Flux: "The Purge".
- "I believe the soul in Paradise must enjoy something nearer to a perpetual vigorous adulthood than to any other state we know. At least that is my hope. Not that Paradise could disappoint, but I believe Boughton is right to enjoy the imagination of heaven as the best pleasure of this world. I don't see how he can be entirely wrong, approaching it that way. I certainly don't mind the thought of your mother finding me a strong young man. There is neither male nor female, they neither marry nor are given in marriage, but, mutatis mutandis, it would be a fine thing. That mutandis! Such a burden on one word!" - Marilynne Robinson, Gilead.]
- "To illustrate the point with trivial stereotypical examples from British society: just as male heterosexuals are free to enjoy themselves playing rugby, drinking beer and talking about girls with their mates, so male homosexuals are to be free to enjoy themselves going to Kylie concerts, drinking exotically coloured cocktails and talking about boys with their straight female mates. Mutatis mutandis – and in many cases the adaptations would obviously be great – the same must apply to other societies. In other words, gay men are to be as free as their straight equivalents in the society concerned to live their lives in the way that is natural to them as gay men, without the fear of persecution."- Lord Rodger of Earlsferry, HJ and HT v Home Secretary, British Supreme Court, 2010
See also 
- Ceteris paribus ("all other things being equal")
- Dependent and independent variables
- List of Latin phrases
- Nunc pro tunc ("now for then", legal term with similar effect)