science

Mutatis mutandis

Mutatis mutandis is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mutatis mutandis rather than just read about it. In short: Mutatis mutandis is a Medieval Latin phrase meaning "with things changed that should be changed" or "once the necessary changes have been made", literally: having been changed, going to be changed. It is used in many countries to acknowledge that a comparison being made requires certain obvious alterations, which are left unstated.

Key takeaways

Mutatis mutandis belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mutatis mutandis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mutatis mutandis from memory before moving on to harder problems.

Reference excerpt

Mutatis mutandis is a Medieval Latin phrase meaning "with things changed that should be changed" or "once the necessary changes have been made", literally: having been changed, going to be changed. It is used in many countries to acknowledge that a comparison being made requires certain obvious alterations, which are left unstated. Mutatis mutandis is still used in law, economics, mathematics, linguistics and philosophy. In particular, in logic, it is encountered when discussing counterfactuals, as a shorthand for all the initial and derived changes which have been previously discussed. It is not to be confused with the similar ceteris paribus, which excludes any changes other than those explicitly mentioned.

Latin The phrase mutatis mutandis—now sometimes written mūtātīs mūtandīs to show vowel length—does not appear in surviving classical literature. It is Medieval Latin in origin and the feet of fines, kept at The National Archives (United Kingdom), contains its first use in England on January 20, 1270, at Pedes Finium, 54 Hen. III, Salop. Both words are participles of the Latin verb mutare ('to move; to change; to exchange'). Mutatus, -a, -um is its perfect passive participle ('changed; having been changed'). Mutandus, -a, -um is its gerundive, which functions both as a future passive participle ('to be changed; going to be changed') and as a verbal adjective or noun expressing necessity ('needing to be changed; things needing to be changed'). The phrase is an ablative absolute, using the ablative case to show that the clause is grammatically independent ('absolute' literally meaning 'dissolved' or 'separated') from the rest of the sentence.

English Mutatis mutandis was first borrowed into English in the 16th century, but continues to be italicized as a foreign phrase. Although many similar adverbial phrases are treated as part of the sentence, mutatis mutandis is usually set apart by commas or in some other fashion. The nearest English equivalent to an ablative absolute is the nominative absolute, so that a literal translation will either use the nominative case ("things changed which are to be changed") or a preposition ("with things to be changed having been changed"). More often, the idea is expressed more tersely ("with the necessary changes") or using subordinating conjunctions and a dependent clause ("once the necessary adjustments are made"). The phrase has a technical meaning in mathematics where it is sometimes used to signal that a proof can be more generally applied to other certain cases after making some, presumably obvious, changes. It serves a similar purpose to the more common phrase, "without loss of generality" (WLOG). The legal use of the term is somewhat specialized. As glossed by Shira Scheindlin, judge for the Southern District of New York, for a 1998 case: "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." In the wake of the Plain English movements, some countries attempted to replace their law codes' legal Latin with English equivalents.

Examples "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

Other languages The phrase appears in other European languages as well. A passage of Marcel Proust's À la recherche du temps perdu includes "...j'ai le fils d'un de mes amis qui, mutatis mutandis, est comme vous..." ("A friend of mine has a son whose case, mutatis mutandis, is very much like yours.") The German Ministry of Justice, similar to the Plain English advocates above, now eschews its use. Their official English translation of the Civil Code now reads:

"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."

In popular culture In Marvel Comics' X-Men series, the phrase is used as the motto of Xavier's School for Gifted Youngsters.

See also Dependent and independent variables List of Latin phrases Nunc pro tunc ("now for then", legal term with similar effect) Substitution

References

Worked examples

Example 1 — a first encounter with Mutatis mutandis

Start with the simplest possible case. Write down what Mutatis mutandis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mutatis mutandis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mutatis mutandis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mutatis mutandis

In research: Mutatis mutandis appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mutatis mutandis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mutatis mutandis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Concepts in logic, Latin legal terminology, Latin logical phrases, so understanding it makes those chapters shorter.
In everyday life: Look for Mutatis mutandis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mutatis mutandis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mutatis mutandis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mutatis mutandis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mutatis mutandis in simple terms?

Why does Mutatis mutandis matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mutatis mutandis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mutatis mutandis.