The most prominent member of the later Academy after Arcesilaus. Carneades was a distinguished sceptic, famous (especially through the report by Cicero) for impressive speeches at Rome on two successive days in either 155 or 156 bc, the first defending justice and its immutable nature, and the second opposing it in favour of expediency. Conservative Romans were duly shocked, and demanded the speedy return of the Athenian delegation in order to protect Roman youths from the influence of the philosophers. His philosophical originality lay in admitting a concept of the plausible (to pithanon), perhaps better thought of as what is acceptable or that which is better to act upon. He needed to fend off the charge that scepticism leads to total paralysis, by defining the kind of reasoning that, in spite of scepticism, remains a suitable basis for action. In this his difficulty anticipated that of later philosophers of science such as Popper, of how to make room for action based on reasonable opinion, given the rejection both of any foundation in certainty and of any increase in the probability of hypotheses via evidence. Carneades voiced a robust rejection of natural theology, anticipating arguments that only re-entered the western tradition with Hume and Kant.