My claim in the thesis is that the Austrians argue for an ontology and an epistemology that have allowed them to develop unique theorems in economics, but that, from Van Til's theistic perspective, these theoretical propositions are claims that cannot be justified by the Austrians.Furthermore, I argue that the capital theory and the interest theory of Mises are those central to the continuing Austrian School. Mises' praxeology is an epistemology developed along the lines of a monistic ontology. However, I claim that Mises did not provide a sound rationale for the important matters of the uniformity of nature, the law of cause and effect, or the logical structure of the human mind; therefore, Mises (and the Austrians) can provide no solution to the philosophical problem of the one-over-many. Mises also asserts that the mind-matter, or subject-object, relation exists; I argue that Mises does not present a sound argument for this proposition but just assumes that it exists.I argue that Van Til's ontology and epistemology provide an answer to these crucial philosophical issues but that the Austrians cannot. This means that the Austrians' economic theorems, particularly those of Mises, do not possess a sound foundation; therefore, their claims to knowledge or truth for their theories of capital and interest are also not able to be justified.The focus of my thesis is the ontological and epistemological groundwork of the Austrian School as it has an impact on the important areas of capital theory and interest theory. However, though I conclude that the Austrians cannot justify the groundwork of their position, this conclusion does not deny the importance of their valuable contributions to capital theory and interest theory.