For example, let's say I am designing a car and I need it to be as light as possible for increased fuel economy but as strong as possible for passenger safety. By making it stronger I make it heavier - by making it lighter I make it weaker. One precludes the other.

So how do I describe this dilemma? Stronger is xxxxx with lighter.

Incompatible, divergent, 'at odds', 'diametrically opposed' all come to mind but none of those are the one I just can't get off the tip of my tongue.

  • Conflicting, antithetical , inconsistent. – user66974 Apr 23 '15 at 21:56
  • 'mutually exclusive'? – Hellion Apr 23 '15 at 22:01
  • All good words - just not the one I am trying to remember. :( It's been two days now... – Tracy Cramer Apr 23 '15 at 22:06
  • It does not quite fit your example sentence but might you be looking for the word “trade-off”? Also, “negatively correlated”, “inversely related” or “inversely proportional”, etc. – Gala Apr 23 '15 at 23:05
  • These are design trade-offs you are trading one for another trying to find the optimal balance. – Jim Apr 23 '15 at 23:42

Preclusive is a word, albeit not one that you are likely to encounter often. It is just the adjective version of preclude.


Conflicting requirements.

One requirement says the car should be strong (hence heavy), the other says it should be fuel efficient (hence light). They are in conflict. Also "competing requirements" may be used.

An interesting follow up question would be, what is a word to describe something that "solves the dilemma" of conflicting requirements? For example, a material that allows the car to meet strength requirements, but is light enough to not compromise fuel efficiency - would mean the requirements for strength and fuel economy are no longer in conflict. A "conflict breaker" if you will.

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