There is no part of the universe where deductive logic is not true (isn't there, do I have the wrong meaning of "true", I don't think I have). Isn't that as simple and clear as it gets.
Its a rule isn't it, just like any law that we could possibly put forward as universal. It may not always be syntactically valid (It cannot be applied to the proposition all dogs are brown), but syntacitical validity is a different thing to truth, isn't it?
I think this question may be
grossly unfounded.
If I was rich (a) I would be happy (b). I am not rich (not a). Now, it cannot be said that because I am not rich I am not happy. Not a therefore not b, is invalid.
If any syllogism was syntactically valid (c) I would be true (d). You cannot say "not c therefore not d". Therefore, there is no deductive argument for the falsity of deductive logic. Not surprising there. Dunno if thats coinvincing, but I wokred it out, so I'll keep it...
In traditional logic propositions construed as having the form 'All S are P' were called universal... like 'all men are mortal'
I assume that this isn't what you have in mind, cos iI could just say that all dogs are dogs.
I guess you have to state whether you mean, universally syntactically valid, when you say "universal".
I gave it a go
What is "truth" What is "universality"