To conclude that the relationship between two variables is causal,there must be an association between the two variables.The presumed cause must precede the presumed effect,and when a control variable is introduced the original association must disappear.

Causal

Relating to cause and effect; implying or concerned with the relationship between causes and their outcomes.

Control Variable

In research, a variable that is held constant to test the relative impact of an independent variable on a dependent variable.

Association

A connection or relationship between two or more variables, where changes in one variable correspond to changes in another.