  Recent investigations have been carried out on critical analyses of beginning
physics teachers confronted with questionable explanations. These studies raise
the question of the choices made by teachers for their teaching once they have
become aware of one (or more) flaw(s) in the explanations analysed. This
presentation will focus on the possible conflicts, for beginning teachers,
between various selection criteria declared for their explanations, including:
appropriateness (from the points of view of internal coherence, logical
completeness and compliance with accepted physical laws) and simplicity. It
will introduce the definition of "mathematical efficiency" as a criterion for
assessing an explanation, on the basis of a study whose results show that it is
a priority for some EDs even at the cost of coherence and of simplicity. The
article concludes with the implications of the issues addressed for research
and teacher training
