Simplex sigillum veri

Question

G. Polya in How to Solve It translates simplex sigillum veri as "simplicity is the seal of truth".* In this discussion on latindiscussion.com, most people seemed to agree that the Latin is wrong: the adjectives should in one way or another be nouns, e.g. veritatis sigillum simplicitas or simplicitas obsignat veritatem.

I'm wondering, is simplex sigillum veri actually correct? I can see two ways to understand it grammatically, as figurative speech:

1. Literally: "Simple is the seal of the true." If the sign that you come across is simple, then the hypothesis that it suggests is likely true. Polya gives an example where, looking at the center of gravity of first a rod, then a triangle, and then a tetrahedron, you notice a simple regularity, suggesting that the pattern continues to any number of dimensions.
   
   This interpretation makes the phrase something like both metonymy and anthropomorphism: when the truth "leaves its mark", that mark is simple. To frame this with simplicitas and veritas would scrap the poetry—the notion that the true, underlying source of all things puts a wax seal upon them, certifying their origin, and its seal is not some complicated, ornate signature, but a simple, unpretentious design.

2. Literally: "Being simple is the seal of being true." Saying simplex and veri instead of simplicitas and veritas would be anthimeria: the figure of speech in which a word is used as a different part of speech than normal for rhetorical effect.
   
   The same figure in English: "Simple is the seal of true." Anthimeria is very common in English today, especially in advertising, but I gather not so common in Latin. Also, I find this figure much less evocative than the previous one, so I'm rejecting it, but I'm still curious if anthimeria here is plausibly good Latin.

Quae interpretatio Latinitatem fert maximam?

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*_{Near the end of the article on "analogy".}

Answer 1

I see no grounds to declare the phrase incorrect in the sense of ungrammatical. I might have had trouble parsing it, as I would instinctively have read simplex as modifying sigillum, but, knowing from the purported English translation the general direction of the idea behind it, it seems clear to me that simplex and veri are simply standalone neutral adjectives used as nouns, and the literal meaning is:

The simple is the mark of the true.

... where we immediately note that "the true" is not just logically the truth, but in fact singular neutral verum is quite frequently used in this sense, e.g. dic mihi verum "tell me the truth," etc. So we really have "the simple is the mark of truth." This seems perfectly understandable and sensible to me, although one might wonder if it is actually, well, true...

Lastly, I think that replacing "the simple" with "simplicity" in English does no violence to the meaning and is safely within the pale of a translator's freedom.