  Online discussion moderators must make ad-hoc decisions about whether the
contributions of discussion participants are appropriate or should be removed
to maintain civility. Existing research on offensive language and the resulting
tools cover only one aspect among many involved in such decisions. The question
of what is considered appropriate in a controversial discussion has not yet
been systematically addressed. In this paper, we operationalize appropriate
language in argumentation for the first time. In particular, we model
appropriateness through the absence of flaws, grounded in research on argument
quality assessment, especially in aspects from rhetoric. From these, we derive
a new taxonomy of 14 dimensions that determine inappropriate language in online
discussions. Building on three argument quality corpora, we then create a
corpus of 2191 arguments annotated for the 14 dimensions. Empirical analyses
support that the taxonomy covers the concept of appropriateness
comprehensively, showing several plausible correlations with argument quality
dimensions. Moreover, results of baseline approaches to assessing
appropriateness suggest that all dimensions can be modeled computationally on
the corpus.
