Causal and Non-Causal Systems

Causal: Output only depends on past or present values of input (no future input)

Examples:

$$\begin{array}{rl}\text{Causal: }& x(t)+x(t-2)\\ \text{Causal: }& x(t)\sin (t+2)\\ \text{Noncausal: }& x(t+1)-x(t)\\ \text{Noncausal: }& x[n+3]+x[n-3]\end{array}$$