  If a person firmly believes in a non-factual statement, such as "The Earth is
flat", and argues in its favor, there is no inherent intention to deceive. As
the argumentation stems from genuine belief, it may be unlikely to exhibit the
linguistic properties associated with deception or lying. This interplay of
factuality, personal belief, and intent to deceive remains an understudied
area. Disentangling the influence of these variables in argumentation is
crucial to gain a better understanding of the linguistic properties attributed
to each of them. To study the relation between deception and factuality, based
on belief, we present the DeFaBel corpus, a crowd-sourced resource of
belief-based deception. To create this corpus, we devise a study in which
participants are instructed to write arguments supporting statements like
"eating watermelon seeds can cause indigestion", regardless of its factual
accuracy or their personal beliefs about the statement. In addition to the
generation task, we ask them to disclose their belief about the statement. The
collected instances are labelled as deceptive if the arguments are in
contradiction to the participants' personal beliefs. Each instance in the
corpus is thus annotated (or implicitly labelled) with personal beliefs of the
author, factuality of the statement, and the intended deceptiveness. The
DeFaBel corpus contains 1031 texts in German, out of which 643 are deceptive
and 388 are non-deceptive. It is the first publicly available corpus for
studying deception in German. In our analysis, we find that people are more
confident in the persuasiveness of their arguments when the statement is
aligned with their belief, but surprisingly less confident when they are
generating arguments in favor of facts. The DeFaBel corpus can be obtained from
https://www.ims.uni-stuttgart.de/data/defabel
