In this extended class discussion, we see the teacher developing an argument with the class for the factors that are essential for rusting. It is interesting to note he makes the strong claim that, "It's got to be an iron nail' for rusting to occur. The information available to the class at this time(that iron nails rust, but copper nails do not) can provide supportive, but not conclusive, evidence for this claim. The teacher is moving beyond the limits of available evidence as be helps the class to identify the essential factors. He also reinterprets their complex factors in terms of these essential factors.