We propose a measure of complexity for symbolic sequences, which is based o
n conditional probabilities, and captures computational aspects of complexi
ty without the explicit construction of minimal deterministic finite automa
ta (DFA). Moreover, if the sequence is obtained from a dynamical system thr
ough a suitable encoding and its equations of motion are known, we show how
to estimate the regions of phase space that correspond to computational st
ates with statistically equivalent futures (causal states). [S1063-651X(99)
11707-0].