  Among the many decisions to be made in their teaching practice, physics
teachers must decide how to explain each particular phenomenon to students.
This study explores student teachers' (STs) decision-making process when
presented with several explanations of a physical phenomenon that might be used
for teaching purposes. During individual interviews, seven STs were offered
three different explanations of how a tensiometer works, all with an accurate
conclusion. They were also supplied with a grid of criteria for critical
analysis. Following in-depth critical analysis of the three explanations in
close interaction with the interviewer, each ST was asked to specify the
criteria for their choice of explanation, for themselves and for university
students. Even after stressing that they valued consistency, some teachers
opted for an explanation for students that they had just described as
inconsistent and/or incomplete. More specifically, their comments revealed
conflicting ideas about the need for consistency and the various forms of
simplicity or incompleteness in a given explanation. The results invite more
explicit consideration of the complex roles of simplicity or incompleteness in
explanations and the importance of this type of interaction during teacher
preparation.
