This thesis sets out an argument in defence of moral objectivism. It takes Mackie as the critic of objectivism and it ends by proposing that the best defence of objectivism may be found in what I shall call Kantian intuitionism, which brings together elements of the intuitionism of Ross and a Kantian epistemology. The argument is fundamentally transcendental in form and it proceeds by first setting out what we intuitively believe, rejecting the sceptical attacks on those beliefs, and by then (...) proposing a theory that can legitimize what we already do believe. Chapter One sets out our intuitive understanding of morality: that morality is cognitive, moral beliefs can be true or false; that morality is real, we do not construct it; that morality is rational, we can learn about it by rational investigation; and that morality places us under an absolute constraint. The chapter ends by clarifying the nature of that absolute demand and by arguing that the critical idea within morality is the idea of duty. In Chapter Two Mackie’s sceptical attack on objectivism is examined. Four key arguments are identified: that moral beliefs are relative to bfferent agents; that morality is based upon on non-rational causes; that the idea of moral properties or entities is too queer to be sustainable; and that moral objectivism involves queer epistemological commitments. Essentially all of these arguments are shown to be ambiguous; however it is proposed that Mackie has an underlying epistemological and metaphysical theory, scientific empiricism, which is hostile to objectivism and a theory that many find attractive for reasons that are independent of morality. Chapter Three explores the nature of moral rationality and whether scientific empiricism can use the idea of reflective equilibrium to offer a reasonable account of moral rationality. It concludes that, while reflective equilibrium is a useful account of moral rationality, it cannot be effectively reconciled with scientific empiricism. In order to function effectively as a rational process, reflective equilibrium must be rationally constrained by our moral judgements and our moral principles. Chapter Four begins the process of exploring some alternative epistemologies and argues that the only account that remains true to objectivism and the needs of reflective equilibrium is the account of intuitionism proposed by Ross. However this account can be developed further by drawing upon number of Kantian ideas and using them to supplement Ross’s intuitionism. So Chapter Five draws upon a number of Kant's ideas, most notably some key notions from the Critique of Judgement. These ideas are: that we possess a rational will that is subject to the Moral law and determined by practical reason; that we possess a faculty of judgement which enables us to become aware of moral properties and that these two faculties together with the third faculty of thought can function to constitute the moral understanding. Using these ideas the thesis explores whether they can serve to explain how intuitions can be rational and how objectivism can be justified. (shrink)