 Moreover, even with respect to variables that can take more than one value, the notion of an intervention or manipulation will not be well-defined if there is no well-defined notion of changing the values of that variable. Suppose that we introduce a variable “animal” which takes the values \(\{\)lizard, kitten, raven\(\}\). By construction, this variable has more than one value, but if, as seems plausible, we have no coherent idea of what it is to change a raven into lizard or kitten, there will be no well-defined notion of an intervention for this variable and being an animal (or being a raven) will not be the sort of thing that can count as a bona fide cause on a manipulability theory. The notion of changing the value of a variable seems to involve the idea of an alteration from one value of the variable to another in circumstances in which the very same system or entity can possess both values and this notion seems inapplicable to the case under discussion.