SVEN-OVE HANSSON and HANS ROTT
BEYOND RECOVERY? A REPLY TO TENNANT
A Critical Discussion
ABSTRACT. In his paper ‘Changing the Theory of Theory Change: Reply to My Critics’,
N. Tennant (1997b) reacts to the critical reception of an earlier article of his. The present
note rectifies some of the most serious misrepresentations in Tennant’s reply.
In Hansson and Rott (1995), it is shown that Tennant (1994), although
written with the intention of exposing the weaknesses of the Alchourrón–
Gärdenfors–Makinson model of belief revision (AGM model for short),
failed to do so due to a series of mistakes and misrepresentations. Tennant
(1997b) replied to this and to a similar criticism by Makinson (1995). In
this note we want to draw attention to the fact that in his reply, Tennant still
(1) does not even begin to relate his arguments to previous, more thorough
treatments of the same issues; (2) attributes to himself what are in fact
standard results and constructions in belief revision theory; and (3) makes
elementary mistakes of logic.
Ad (1). In Hansson and Rott (1995), it was pointed out that Tennant’s
criticism of the recovery postulate adds nothing new to the criticism that
was voiced earlier by, e.g., Makinson (1987), Fuhrmann (1991), Hans-
son (1991, 1992), Levi (1991), Lindström and Rabinowicz (1991), and
Niederée (1991). In contrast to Tennant, these authors neither claim that
recovery is the ‘main foundation stone’ of the AGM theory of belief re-
vision nor that it can be ‘shown’ to be generally false.
1
But, again in
contrast to Tennant, they constructively show how to accommodate these
arguments and avoid recovery in a precisely defined framework that is still
faithful to many of the basic ideas of AGM. Tennant’s only comment on
this is: “if other writers had indeed already made point (1) [that recovery
can be shown to be false] before me, the fact remains that these writers
did not follow up where their counterexemplary intuitions led them . . . ”
(1997b, p. 573, our emphasis). It is difficult to believe that this could have
been written by someone who has read the above-mentioned papers and
considered the arguments advanced in them.
Erkenntnis 49: 387–392, 1998.
© 1998 Kluwer Academic Publishers. Printed in the Netherlands.