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Mutatis mutandis is a Latin phrase meaning "by changing those things which need to be changed" or more simply "the necessary changes having been made". The term is used when comparing two situations with a multiplicity of common variables set at the same value, in which the value of only one variable is allowed to differ – "all other things being equal" –thereby making comparison easier (cf. ceteris paribus).

It carries the connotation that the reader should pay attention to the corresponding differences between the current statement and a previous one, although they are analogous. This term is used frequently in economics, philosophy and in 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.

Examples

• A local chapter of a national organization may adopt a rule that the national organization's procedure for something will apply, mutatis mutandis, to the local chapter. Thus, even though the chief officer of the national organization may be called the "president", and the chief officer of the local chapter may be called the "chairman", instances of "president" would be changed to "chairman" when applying the national procedure. This is commonly done by subordinate units (such as localities or chapters) to avoid duplication of text in local ordinances or rules that is sufficiently covered by state or national laws or rules.
• "His cat" and "His dog" should be changed to "Her cat" and "Her dog", mutatis mutandis for pony, sheep and cow. (That is, "His pony" becomes "Her pony", and so on.)
• What we said about oil goes mutatis mutandis for natural gas.
• The two parties finally signed the contract mutatis mutandis.
• 1982 Convention in Jamaica (The law of the sea), ARTICLE 111: Section 2. The right of hot pursuit shall apply 'mutatis mutandis' to violations in the exclusive economic zone or on the continental shelf, including safety zones around continental shelf installations, of the laws and regulations of the coastal State applicable in accordance with this Convention to the exclusive economic zone or the continental shelf, including such safety zones.

Etymology

Both "mutatis" and "mutandis" come from the Latin verb "muto" (principal parts: muto, mutare, mutavi, mutatum), meaning "to change." Mutatīs is the perfect passive participle (ablative plural neuter), literally "having been changed." Mutandīs is the gerundive (ablative plural neuter), literally "being about to be changed."

Used as a substantive plural it means "the things that have changed" and the gerund gives the idea of necessity, meaning, "things which need to be changed". The phrase is an ablative absolute construction, which is reflected by the "with" given in the full translation, "with those things having been changed which need to be changed."

The construction is not valid in Classical Latin, where the gerundive was not employed as a noun in plural neuter, except in the nominative or accusative cases (aut facere scribenda aut scribere legenda, "either to perform deeds worthy of description or to write about deeds worthy of being read"^[1]. It is therefore probably of mediaeval origin. The Oxford English Dictionary states that its first instance in British Latin is from 1272.

Contrast with ceteris paribus

Mutatis mutandis is similar to ceteris paribus. Where the latter serves to hold all other things constant to emphasize the effects of one change, mutatis mutandis often serves to suggest (or require) a set of changes which may (or shall) be made without loss of validity.

Quotes

• "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.

See also

• Nunc pro tunc ("now for then", legal term with similar effect)
• List of Latin phrases

References