4.0 Abstract Measurement theory (= quantum language ) is formulated as follows. \[ \underset{\mbox{ (=quantum language)}}{\fbox{pure measurement theory (A)}} := \underbrace{ \underset{\mbox{ (\(\S\)2.7)}}{ \overset{ [\mbox{ (pure) Axiom 1}] }{\fbox{pure measurement}} } + \underset{\mbox{ ( \(\S \)10.3)}}{ \overset{ [{\mbox{ Axiom 2}}] }{\fbox{Causality}} } }_{\mbox{ a kind of incantation (a priori judgment)}} + \underbrace{ \underset{\mbox{ (\(\S\)3.1) }} { \overset{ {}}{\fbox{Linguistic interpretation}} } }_{\mbox{ the manual on how to use spells}} \] Measurement theory says that

$\bullet$ | Describe every phenomenon modeled on Axioms 1 and 2 (by a hint of the linguistic interpretation)! |

**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**