Having hope is important for motivation and human agency, especially when it is certain. People with unwavering hope are more likely to succeed in their endeavours than those without. However, in modern debates, hope is usually seen as characterised by vain optimism. Thomas Aquinas, in contrast, argues that the virtue of hope is characterised by certainty – a view that could contribute significantly to these debates. Nevertheless, there seem to be problems with Aquinas’ view. He says that, while certainty essentially concerns the cognitive faculties, it can also concern other faculties by participation, insofar as the cognitive faculties influence them. He adds that hope can only be said to be certain by participating in the certainty proper to faith. But this reference to the certainty of faith and the cognitive faculties seems to imply that faith is endowed with conclusive evidence, since it is this evidence that enables the cognitive faculties to attain certainty. And throughout his writings, Aquinas denies that faith enjoys conclusive evidence. In this article, I will show that one can resolve this difficulty by understanding that for Thomas faith is indeed an intellectual act, but its certainty is different from the certainty of reason. This will enable us to gain an understanding of Aquinas’ view of the certainty of hope, as well as other aspects of his reflections on hope and faith.