jats:titleAbstract</jats:title>jats:pTestimony is a source of knowledge. A speaker asserts what a hearer may therefore come to know. Assertion has widely been treated as the exclusive or at least the paradigmatic vehicle for testimony. I argue that we testify not only by asserting something, but also by taking something for granted within some other utterance. In philosophy of language, this is called semantic presupposition. The very reasons leading theorists of testimony have for thinking that assertion can be testimony are equally reasons for thinking semantic presupposition can be testimony.</jats:p>