Proof, the essence of mathematics, started from conjecture. Conjecture and proof or justification in the behavior
of mathematicians are not a separate process but the latter is reached through the former. The goal of this study is to examine in
what methods and chances the mathematics textbooks for the second grade in middle school provide the conjecture activities to
the students and how justification is introduced. Four thinking methods(perception, induction, analogy, abduction) and four
chances (observation, construction, transformation, reflection) were integrated, and the justification stages of Kim Jeong-ha
(2010) were recomposed. The results of this study are as follows. First, the conjecturing tasks mostly involved perceptual and
abductive reasoning in the investigation activities and provided the chances of observation. Chances of reflection were rare and
chances of transformation were not utilized. The conjecturing tasks involving only perception and inductive conjecturing provided
just the chances of observation or construction, and analogic conjecturing tasks and abductive conjecturing tasks provided
the chances of reflections. Second, justification explanations of the textbooks all introduced formal justifications.