# Difference between satisfy and fulfill

Writing a mathematical text I came across a site that lists some common mistakes when writing scientific texts in English including the following:

x fulfills property P
x satisfies property P

I am now very confused since I read this (the “wrong” usage) quite a few times in various papers (and I can't remember a single one were the “correct” word is used). I also found this site stating

The difference between satisfy and fulfill is that satisfy is to […] fulfill (wishes, requirements) […]

fulfill: […] To satisfy, carry out, bring to completion (an obligation, a requirement, etc.).

which gives me headache explaining satisfy with fulfill and vice versa.

So what is the difference between satisfy and fulfill? In particular I want to know what to use when I want to express that a condition must be satisfied / fulfilled?

The specific examples where I want to use one of these words:

1. The angles satisfy / fulfill the condition…
2. The vectors satisfy / fulfill the inequalities…
3. This condition has to be satisfied / fulfilled for every vertex.

I don't think these are very different, but just in case. Thanks.

• Unfortunately, this seems to have little to do with dictionary definitions and more to do with what is customary in the field -- which means it's less about understanding why and more about memorizing what is most common. There is no reason why satisfy is correct and fulfill is not, other than "this is how it's done". Jul 5, 2017 at 16:40
• But satisfy is “how it's done” – at least in the above examples? Jul 5, 2017 at 16:47
• @spettekaka: Then what's your problem? If you know how a certain word is used, you know how it's used. Are you saying this bothers you beyond that? Jul 5, 2017 at 17:36
• I would use satisfy for all three of your examples. You won't be misunderstood. If you are talking about predictions, you may use fulfill. Jul 5, 2017 at 18:06
• Language-wise, satisfy meets certain conditions, while fulfill meets all conditions. As this is strictly a math context, you might ask this on Mathematics SE Jul 5, 2017 at 18:41

Satisfy has these two Latin words as a root (from Google):

late Middle English: from Old French satisfier, formed irregularly from Latin satisfacere ‘to content,’ from satis ‘enough’ + facere ‘make.’

whereas fulfill has this etymology:

late Old English fullfyllan ‘fill up, make full’ (see full1, fill).

When something is full, putting more in will make it overflow.

So satisfy implies that there is a minimum to consider good, but you could do more to improve things further than the minimum.

Fulfill implies that either you achieved a standard (reached the "full" line") or did not. There is really no such thing as "halfway fulfilled," for example.

This is why things like destinies or orders are fulfilled, but not satisfied. Either you reached your destiny or you didn't, either your order is complete or it is not. But you could satisfy an indignant customer who didn't get an order fulfilled by giving him/her a gift card, though a higher amount gift card would make him/her more satisfied.

• Nice answer, thanks. So with this I think fulfill is the better variant for my examples, since all conditions should be fulfilled and not just some. Or what do you think? I am still not 100 % sure. Jul 9, 2017 at 13:59
• Then, speaking about a doctoral thesis... Would you say "authorizes for submission since it fulfils the conditions necessary for its defence" or "satisfies"?
– skan
Oct 27, 2020 at 13:38