Terry's argument: Terry starts with two premises. First, some actions our society considers bad actually have favorable consequences. Second, an action is good only if it has favorable consequences. From these, Terry concludes that some actions our society considers bad are actually good.

Pat's argument: Pat agrees with Terry's conclusion but offers different reasoning. Pat's first premise is that some good actions don't have favorable consequences. Pat's second premise is that no actions considered bad by our society have favorable consequences. From these, Pat also concludes that some actions our society considers bad are actually good.

Terry's flaw: Terry's second premise says that favorable consequences are necessary for an action to be good. In other words, good → favorable consequences. But Terry uses this premise as though favorable consequences are sufficient for an action to be good.

Terry's first premise establishes that some actions considered bad have favorable consequences, and Terry jumps from there to the conclusion that those actions are good. But having favorable consequences doesn't guarantee that an action is good. It just means that if an action is good, it will have favorable consequences. An action could have favorable consequences and still not be good if there are other requirements for being good that haven't been met.

Pat's flaw: Pat commits the same type of error but using a different conditional premise. Pat's second premise tells us that if an action is considered bad, it does not have favorable consequences. In other words, considered bad → no favorable consequences. But Pat reverses this conditional by treating "no favorable consequences" as though it guarantees an action is considered bad.

Pat's first premise says some good actions lack favorable consequences. By reversing the conditional, Pat treats those good actions that lack favorable consequences as though they must be considered bad by our society, giving Pat the conclusion that some actions considered bad are good. But lacking favorable consequences doesn't guarantee an action is considered bad. Actions could lack favorable consequences without our society having any opinion about them at all.

So both speakers reach the same conclusion, and both make the same type of logical error: confusing a necessary condition for a sufficient one. Terry reverses "good → favorable consequences," and Pat reverses "considered bad → no favorable consequences."