1. A B C. This junction is the simplest example of a “chain,” or of mediation. In science, one often thinks of B as the mechanism, or “mediator,” that transmits the effect of A to C. A familiar example is Fire Smoke Alarm. Although we call them “fire alarms,” they are really smoke alarms. The fire by itself does not set off an alarm, so there is no direct arrow from Fire to Alarm. Nor does the fire set off the alarm through any other variable, such as heat. It works only by releasing smoke molecules in the air. If we disable that link in the chain, for instance by sucking all the smoke
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