  A popular view in contemporary Boltzmannian statistical mechanics is to
interpret the measures as typicality measures. In measure-theoretic dynamical
systems theory measures can similarly be interpreted as typicality measures.
However, a justification why these measures are a good choice of typicality
measures is missing, and the paper attempts to fill this gap. The paper first
argues that Pitowsky's (2012) justification of typicality measures does not fit
the bill. Then a first proposal of how to justify typicality measures is
presented. The main premises are that typicality measures are invariant and are
related to the initial probability distribution of interest (which are
translation-continuous or translation-close). The conclusion are two theorems
which show that the standard measures of statistical mechanics and dynamical
systems are typicality measures. There may be other typicality measures, but
they agree about judgements of typicality. Finally, it is proven that if
systems are ergodic or epsilon-ergodic, there are uniqueness results about
typicality measures.
