Why a system is causal if the impulse response is zero for \$t<0\$?

Question

I was reading a definition that

Suppose \$h(t)\$ is the impulse response of any system \$Y\$, then the system is causal if and only if \$h(t)=0\$ for \$\forall t<0\$

I know what a causal system is, but I don't understand it in terms of the impulse response. And I was wondering why is it causal here?

Possible duplicate of [Meaning of causal signal](https://electronics.stackexchange.com/questions/79824/meaning-of-causal-signal) — Maxim, Apr 17 '19 at 20:48

score 4 · Accepted Answer · answered Apr 17 '19 at 20:08

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Causal systems are systems where the output only depend on past/present inputs. The impulse happens at time t=0, so if the output isn't zero prior to t=0 then it depends on a future input.

answered Apr 17 '19 at 20:08

Charles H

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Why a system is causal if the impulse response is zero for \$t<0\$?

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