Washington Röbling’s Implicature

Speranza

The trustees are considering naming the Washington Roebling chief engineer.

TRUSTEE: 

You have never supervised anything of this scale and magnitude, Roebling, is that right?

ROEBLING: No one has.

H. P. Grice considers this in his Oxford lectures on conversational implicature (yes, he was using that phrase, 'conversational implicature' back then -- BEFORE Harvard).

Surely, Washington Roebling is being more informative than is required.

The implicature is:

Tricky!

Trustee: 

You have never supervised anything of this scale and magnitude, Roebling, is that right?

ROEBLING: 

No one has.

Roebling's

(i) No one has.

ENTAILS an affirmative answer to the question, to wit:

(ii) Washington Roebling has never supervised anything of this scale and magnitude.

Or strictly:

(iii) Yes, that is right: Washington Roebling has never supervised anything of this scale and magnitude.

By uttering something slightly more informative, "in fact, no one has" IMPLICATES something. 

What?

(iv) Neither have you!

Or more polite:

(v) Why do you axe?

Tricky!

The greatest implicature is that Washington is a Griceian at heart.