**
Abstract (Chap. 10; Axiom 2 ( Causality ))
**

Measurement theory has the following classification:

$(A):$ | $ \underset{(=\mbox{ quantum language})}{\mbox{ measurement theory}} \left\{\begin{array}{ll} \underset{\mbox{(A$_1$)}}{ \mbox{pure type}} \left\{\begin{array}{ll} \!\! \mbox{classical system} : \mbox{ Fisher statistics} \\ \!\! \mbox{ quantum system} : \mbox{ usual quantum mechanics } \\ \end{array}\right. \\ \\ \underset{\mbox{(A$_2$)}} {\mbox{mixed type}} \left\{\begin{array}{ll} \!\! \mbox{ classical system} : \mbox{ including Bayesian statistics,} \\ \qquad \qquad \qquad \mbox{ Kalman filter} \\ \!\! \mbox{ quantum system} : \mbox{ quantum decoherence } \\ \end{array}\right. \end{array}\right. $ |

**What is causality?**

**Again recall that, as mentioned in $\S$1.1, the main purpose of this book is to assert the following figure 1.1:**

**Fig.1.1: the location of "quantum language" in the world-views**