Comment by jiggawatts

My understanding is that they’re generally treated as homonyms in most cases but some philosophers like to use OUGHT in a moral sense and SHOULD as practical advice to achieve an OUGHT.

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.