the possibility of pure altruism and advanced the doctrine of psychological egoism, while others (Butler, Hume, Rousseau, Adam Smith, Nagel) argued for the existence of altruistic motives. Conceptually, the warm-glow model represents a stylized compromise between these two perspectives, allowing for individuals to be purely altruistic, purely egoistic, or impurely altruistic. Warm glow is at least tangentially related to the topic of free will, as people should only reap the psychological reward of helping if they freely choose to do so. Background in economics Departure from Classical theory The normative theory of Ricardian equivalence suggests private spending should be unresponsive to fiscal policy because forward-looking individuals smooth their consumption, consistent with Modigliani's life-cycle hypothesis. Applied to the provision of charities or public goods, Ricardian equivalence and the classical assumption of pure altruism together support the neutrality hypothesis, implying perfect substitutability between private and public contributions. The neutrality hypothesis assumes rational economic agents are indifferent to whether a cause is funded by the private or public sector; only the level of funding is relevant. A consequence of neutrality under perfect altruism is that government grants should completely crowd-out private donations. That is, a dollar given by the government takes the place of a dollar that would have been given by a private citizen. To illustrate, economic agents operating under the neutrality hypothesis would give to a cause until complete provision, beyond which they would contribute nothing. This is consistent with Andreoni's conceptualization of "pure altruism"; however, it is inconsistent with impure altruism or pure egoism. Thus, warm glow and the failure to act as purely altruistic present fundamental challenges to the neutrality hypothesis and Ricardian equivalence. In economics, violations to the neutrality hypothesis pose serious concerns for macroeconomic policies involving taxation and redistribution; and microeconomic theories for collective action and public good provision. Several of Andreoni's contemporaries simultaneously provided evidence against neutrality-driven crowding-out effects, including Kingma (1989) and Khanna et al. (1995). Taken together, these findings offered a strong rebuke of the assumption that public grants crowd-out private donations to public goods. Original model Andreoni's economic model of impure altruism considers a simplistic world with only two goods: a private good and a public good. A given individual, endowed with wealth faces the budget constraint: where represents consumption of a private good, and represents the contribution to the public good. To the extent that positively contributes to utility, it may be