Passage Summary: If you unplug a mouse, the programs that need it won't work. Fred's programs aren't working, so he must have unplugged the mouse.

Conclusion: The mouse on Fred's computer must have become unplugged.

Reasoning: Unplugging a mouse makes mouse-dependent software fail, and since Fred's mouse-dependent software has failed, the mouse must be unplugged.

Analysis: This argument suffers from a classic formal logic error known as affirming the consequent. While unplugging the mouse is a sufficient condition to break the software, it is not a necessary one; Fred's software could be failing for a dozen other reasons. Perhaps the mouse is simply broken, the USB port is dead, or there is a software glitch. Look for an answer that points out the argument treats a possible cause as the only possible cause.