Studying AR models, I found that there are two properties that these models can have stationarity and causality.
For what concerns stationarity, I have studied that this condition is satisfied if the equation $\phi(B) = 0$ has all roots outside the unit circle, i.e. they are in modulus greater than one.
Instead, for what concerns causality, I am having some troubles: I mean, the conditions for causality seem to me the same of stationarity (at least for what concerns simple $AR(1)$, $AR(2)$). Moreover, I am not sure of having understood what does causality actually mean.
Increasing my doubts, I have also found that some people talk about an invertibility condition for $AR$ models, but I have understood that it was only concerning $MA$ models and that it is a kind of counterpart for stationarity, given the fact that $MA$ are always stationary.
Could you help me making a bit of order in my mind?