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