I apologize if this is an obvious question, but I have not been able to find the answer in a dictionary.

The specific problem I'm having is distinguishing between

[certificate] which certifies the suitability of a product for [purpose] vs. [certificate] which certifies the fitness of a product for [purpose].

Personally I feel suitability has a slightly more positive bias, but at the same time might be less rigorous, while fitness seems more rigorous but also more neutral.

If anyone can explain the exact difference between these two I would be much obliged.

  • 1
    These two words mean nearly the same thing here. And while some people may perceive a difference, I expect they're close enough that different people may have different views of this difference. Commented Jun 8, 2015 at 12:29

2 Answers 2


Here are the definitions, not for products but for human competence, according to the DOD.

What is Suitability? Suitability refers to a person’s identifiable character traits and conduct sufficient to decide whether employment or continued employment would or would not protect the integrity or promote the efficiency of the service.

What is Fitness? Fitness refers to the level of character and conduct determined necessary for an individual to perform work for, or on behalf of, a Federal agency as an employee in the excepted service (other than in a position subject to suitability) or as a contractor employee.

If I understand well, and adapted for a product, suitability, would be, for example, that a knife is suitable to cut a steak (whatever the state of its blade) but could not be called fit to cut the steak if it's not sharp enough to do the job.

See also this reference about commercial transactions and fitness vs suitability in the Australian legal system: sydney.edu.au/law/slr/slr_32/slr32_2/Pearson.pdf.

It's might be confusing though. The author seems to say that suitabilty is the continuation, a more modern verson of fitness but in the body of the text he sometimes uses the term as synonyms...

  • P. Obertelli's definitions have a distinctly legal and even HR flair. Fitness also has a biological and ecological meaning which refers to an organisms ability to survive in its given environment, it's fitness. This is not the same thing as suitability, which doesn't have the same ecological skew.
    – user57832
    Commented Jun 8, 2015 at 15:01
  • @mike hunter actually, suitability does seem to have an ecological connotation: try googling for "environment/ecological suitability " you'll see millions of hit. To make short "this animal is fit for this environment" but an "this environment is suitable for this animal"
    – P. O.
    Commented Jun 8, 2015 at 15:20

physical or mental or emotional or spiritual but fitness relates to the norms or protocols or nature of human perfection ,this perfection is the highest reach.the second one reaches to the first and fits into it..shows fitness,whereas suitable is a little bit of diluted.which leads to matching of first and second one,the highest approximity of matching is referred as suitability.in fitness there is no matching..

  • uhhhh... what? (This looks like it's supposed to be an answer, but I can't make any sense out of it.)
    – Hellion
    Commented Nov 13, 2015 at 15:55

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