I'm too lazy to look it up just now, but roughly Engels's point was that though "the human mind" might be capable of achieving universal truth, that "human mind" existed in the form of very limited particular minds. I think it is in that context that he says something like what you say below: the assumption that the world is a unity cannot be demonstrated except by total knowledge (which is a long way off). He said it better.
Carrol
James Culbertson wrote:
>
> Of course to absolutely Know that the first is false (or the 2nd is
> true) you'd have to have perfect knowledge of all that is.
>
> James
>
> Carrol said,
> >1. The human mind can achieve perfect knowledge of all that is.
> >
> >2. Humans will always discover new things.
> >
> >Only the first is false. To deny the second is in fact to affirm the
> >first. Engels's ironic treatment of Duhring's claims to absolute
> >knowledge is good on this.
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