Subject Matter

• Air pressure exists all around us.
• While individual molecules that make up the air bounce all around and push as they collide into things, the collective result, air pressure, is passive. Air pressure doesn't actively push on things, it just exists around them, forming a boundary in an omnidirectional sense. A common mistake is to think of air pressure as an active force pushing down in one place and in one direction (usually down).

Causality

• Some causal agents behave passively to result in effects.
• It can be difficult to notice passive causes. Causal agents that are perceived as "active" are more likely to be recognized.
• Being unaware of passive causes can limit the scope of variables that we consider as possible explanations for events around us.