In ''Conservatism'' (2011), O'Hara developed the philosophy of 'small-c conservatism' that he outlined in ''After Blair'' (2005/7). He argued that conservatism must be a philosophy concerned with social change, and must be defensible using public reason. To that end, he defined conservatism as the knowledge principle plus the change principle. The knowledge principle, influenced by scepticism, states that:
“because society and its mediating institutions are highly complex and dynamic with natures that are constantly evolving as they are co-constituted with the individuals who are their members, both data and theories about society are highly uncertain”.
The change principle adds:
“because the current state of society is typically undervalued, and because the effects of social innovations cannot be known fully in advance, then social change (a) must always risk destroying beneficial institutions and norms and (b) cannot be guaranteed to achieve the aims for which it was implemented. It therefore follows that societies should be risk-averse with respect to social change, and the burden of proof placed on the innovator, not his or her opponents. It also follows that change, when it does come, should ideally be (a) incremental, (b) reversible where possible and (c) rigorously evaluated before the next incremental step”.
Influenced by Edmund Burke, Adam Smith, Michael Oakeshott and Friedrich Hayek, O'Hara distanced conservative philosophy from free-market liberalism and neoconservatism. He also developed ideas about risk and uncertainty about the environment to sketch a type of green conservatism.
