From: Philip Johnson-Laird BA PhD Psychology (UCL), Stuart Professor of Psychology Emeritus at Princeton. (Author isn't a logician.) How We Reason (1st edn 2008). p. 128.

I can't format the page with StackExchange's tools. Thus a screenshot:

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The sentence underlined in green is the last one that I understand. Thus the table up to it is:

enter image description here


I agree that the explanation is a little obtuse...

Given that "Bertie who is Mr Hardy's neighbor doesn't drink Bass", Bertie can't be the Bass drinker. Bertie and John are both first names, so they can't refer to the same person. So Bertie is not John, nor the Bass drinker.

The highlighted red sentence should not begin with "Hence", since we only take into account the green sentence in conjunction (and not as a premise) with realizing the above facts. Here is a rewrite of that sentence:

"Also, Bertie is not John nor the Bass drinker, and hence he must be Russell."

  • 2
    $\begingroup$ Suggested improvement: "The explanation is confusing because of the inclusion of the word 'Hence'." $\endgroup$ – shoover Jul 10 '18 at 3:53
  • 1
    $\begingroup$ Good point! Thank you, I've added a note to my answer to address that. $\endgroup$ – humfuzz Jul 10 '18 at 16:54

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