Final answer:
The statement is true; Ayn Rand was an ethical egoist, advocating rational self-interest as morally correct, but she was not a psychological egoist, which posits that all human actions are fundamentally self-serving.
Step-by-step explanation:
The statement that Ayn Rand was an ethical egoist but not a psychological egoist is true. Ethical egoism is the normative theory that the promotion of one's own good is in accordance with morality. In Rand's view, individuals should act in their rational self-interest and this does function as the moral groundwork for actions. This is supported by Anscombe's critique of modern moral philosophies, which often lack a firm foundation for their 'oughts' and rely on a legislator, such as God in theistic philosophies.
On the other hand, psychological egoism is a descriptive theory that suggests that humans always act in their own self-interest, even when they seem to be acting altruistically. This concept was notably discussed by Nietzsche, and objections to it highlight that humans can act contrary to their self-interest or with altruistic intentions.
Egoism and ethical debate intermingle when considering the common good and the nature of altruism within moral philosophy. Arguably, ethical egoism does not necessarily preclude the possibility of acting in ways that benefit others as a secondary effect of pursuing one's self-interest.