Passage Summary: Yang argues that because ancient people used bread-rising agents, they must have used yeast. Campisi points out that yeast isn't the only thing that makes bread rise, so Yang's conclusion is a bit of a stretch.

Conclusion: Campisi concludes that Yang's specific inference regarding the use of yeast in 1200 B.C. is not necessarily valid.

Reasoning: There were other substances known to act as leavens during that time period besides yeast.

Analysis: Focus strictly on the structure of the exchange. Campisi identifies a flaw in Yang's logic by introducing an alternative possibility that Yang overlooked. Yang assumes that because a general category (leavens) was present, a specific member of that category (yeast) must have been the one used. It’s a classic case of someone being a bit too confident in their specific guess when other options are still on the table.