I feel "ought" is stronger and is something that is expected of you, but English is not my native language.
"You should drink more water"
"You ought to help your sick mother"
"You should drink more water"
"You ought to help your sick mother"
But there is significant overlap.
You'll also need RFC 6919[1] for "OUGHT TO":
> The phrase "OUGHT TO" conveys an optimistic assertion of an implementation behavior that is clearly morally right, and thus does not require substantiation.
And the up-threads gut feel that "ought to" is slightly stronger comes across there, I think: ought to conveys that moral stance, where as "should" is more "there's a decision here, possibly".
[1]: https://www.rfc-editor.org/rfc/rfc6919.html; n.b., this is an April 1st RFC. I like it, though, and it isn't uncommon to see a stray "ought to" lacking a citation in a non-April-1st RFC.
Hence OUGHT leads to SHOULD and the latter is meaningless without the former.
E.g.: You OUGHT to secure systems that handle sensitive customer data, so you SHOULD regularly patch your software.
Just telling someone they should do something without an initial moral motivation to do the “right thing” can fall on deaf ears.
I’ve seen an official patch management strategy in a government organisation that was simply: “Don’t”.
Their moral argument was that they OUGHT to save taxpayer money and so they SHOULD save time, money, and effort by not applying updates (which they felt weren’t necessary for security).
In other words: OUGHTs are like axioms that you can choose, and then the SHOULDs derive from them automatically.
Also fun: yesn’t. Yes, but really no.