Tibor R. Machan, Eric Mack, and Douglas B. Rasmussen present three differing analyses of Rand's view that the "choice to live" serves as the foundation of her ethical system. Hartford criticizes Machan's view that the choice is a "fundamental commitment." Hartford concludes that Rasmussen's assertion—that individual self-perfection is the natural end of human choice—cannot validate the choice to live. Hartford claims that Mack's analysis of the "function of valuing" as a bridge of the factual-normative gap can be strengthened. Hartford argues that carefully defining the meaning of "the choice to live" allows proof of its validity.