Forces always occur in equal but opposite pairs. This is known as Newton's Third Law of Motion.

Here's a breakdown:

* Equal: The forces have the same magnitude (strength).

* Opposite: The forces act in opposite directions.

* Pairs: For every force acting on an object (the action force), there is an equal and opposite force acting on a different object (the reaction force).

Example:

* Action: You push on a wall with your hand.

* Reaction: The wall pushes back on your hand with an equal and opposite force.