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What is the difference between 'mandatory' and 'indispensable'? Can we use them interchangeably? Are there examples which show the difference between both words?

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"Mandatory" means that the thing must be done due to some reason or rule.

These courses are mandatory.

That is, you must take the courses or else you fail.

Wearing helmets was made mandatory a few years ago.

It is a rule that you must wear helmets.


"Indispensable" is that the thing is so critical, useful, or important that you cannot conceivably throw the thing away.

The volunteers' help was indispensible.

The mission would have failed if the volunteers didn't help.

He made himself indispensible to the parish priest.

He was deemed a must-have person because of some good quality.

These great tools are so versatile that they are indispensable.

The tools are so good that you shouldn't be without them.


To sum up, these two words are not interchangeable - they have their own distinct meanings.

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    Simple example: It is mandatory to have a driver's license to drive. I once drove for about 3 months with my driver's license sitting in a drawer at the library--they forgot to return it, I didn't realize I didn't have it with me. It certainly wasn't indispensable! – Loren Pechtel Dec 3 '15 at 19:25
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    @LorenPechtel, While a driver's license is mandatory, fuel is indispensable. – Ron Jensen Dec 3 '15 at 20:13
  • "The mission might have failed" If it might have succeeded without the volunteers, they weren't indispensable, only very valuable. "Would" gives the meaning more clearly – the help was instrumental to the success of the mission. – Nic Hartley Dec 3 '15 at 20:20
  • @RonJensen, Tesla would disagree with that. :-) – cjm Dec 3 '15 at 20:23
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    @cjm I said fuel instead of gas hoping it would include electrons. :-) – Ron Jensen Dec 3 '15 at 20:40
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Very few (if any) words are truly interchangeable, and these two are rarely interchangeable. Both "mandatory" and "indispensable" roughly mean "necessary". But they are used in completely different situations.

"Mandatory" has the nuance of "necessary because of rules and regulations created by someone/group of people" and is usually used with things one must do. e.g.

  • mandatory attendance
  • mandatory minimum sentences for crimes
  • a mandatory meeting

The connotation is neutral to negative. I could imagine a high-school student saying, "Ugh! why is it mandatory that we take 4 years of Math?"

"Indispensable" on the other hand has the nuance of "necessary because other things would fail without it". It is usually used with essential elements of an entire collection of things.

  • An indispensable team member
  • An indispensable ingredient
  • An indispensable tool

The connotation is usually positive.

  • +1, but I wouldn't say that "mandatory" is "negative". If you agree with a rule you might think it quite positive. – Jay Dec 3 '15 at 14:38
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    @Jay I think the slightly negative connotation of "mandatory" is related to the fact that there is some kind of mandate for the mandatory thing. If everyone wanted to do the mandatory thing on their own, there would be no need for a mandate to be issued to make the thing mandatory. Therefore, when something has been made mandatory, it's often despite the fact that people don't want to do it, not because most people do want to do it. "Indispensible" connotes something that cannot be dispensed with, meaning it's already being used and is needed so much one couldn't stop using it. – Todd Wilcox Dec 3 '15 at 15:51
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    +1, I would add that "mandatory" doesn't simply have that nuance, but the actual etymological definition, as it derives from mandate: an official order or commission to do something – Sabre Dec 3 '15 at 15:52
  • @Sabre Exactly, and as I mention in my earlier comment, "indispensible" also has a built-in etymology from dispense: to throw away or do without. – Todd Wilcox Dec 3 '15 at 15:54
  • @Sabre True, but be aware of the etymological fallacy. – R.M. Dec 3 '15 at 16:43

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