The Nachlass of A.N. Prior
a joint project between
Department of Information Studies - University of Copenhagen
and
Department of Communication and Psychology - Aalborg University

The problem of the two babies

By Arthur N. Prior on NA/NA/NA

It has been transcribed and commented on by Zuzana Rybaříková and David Jakobsen

Download the PDF of this item
Please note that this text is extracted from the PDF, and is as such most likely not styled properly.
The problem of

the
two babies
1

There are two babies, Peter and Robert, born at the same time in the same hospital. Their mothers
are Mrs. Smith and Mrs. Jones, but it is not known which baby belongs to which mother. The father
of Mrs. Jones' baby is Mr. Jones. The father of Mrs. Smith's

baby is either Mr. Smith
or Mr. Jones,
but no one else. A

baby both of whose parents have blue eyes always has blue eyes. Mrs. Smith,
Mr. Jones, and Peter all have blue eyes, while Mr. Smith, Mrs. Jones, and Robert all have brown
eyes. Blood tests show t
hat Robert can be Mrs. Smith's child only if Mr. Jones is his father.

Use the above information to assign each baby to the correct mother and if possible to the
correct father.
2




1

Editor
s


n
ot
e: The
MS

is located at the Pri
or archive
, box 11,

at t
he Bodleian Library in Oxford
.

It has been
transcribed and commented
on
by Zuzana
Rybaříková

and David Jakobsen.
The text is handwritten, but not in P
rior

s
hand. The paper is probably Canterbury note paper. It is likely that the text is an exercise for one of Prior

s logic
classes.

The
title has been added by the editor
s
.

2

To find more information about paternal testing
back

in Prior’s t
ime see G. A. F. Seber (1985): Use of blood samples
in paternity testing and forensic science, Journal of the Royal Society of New Zealand, 15:2, 157
-
168.

  www.priorstudies.org •  University of Copenhagen •  Aalborg University •