Even more on Fine Tuning

The central portion of the Fine Tuning Argument (FTA) is valid: Assuming that $\mathit{P}\left(\mathit{L}|\mathit{C}\right)=1$ by definition, then $\mathit{P}\left(\mathit{C}|\mathit{L}\right)=\frac{\mathit{P}\left(\mathit{L}|\mathit{C}\right)\mathit{P}\left(\mathit{C}\right)}{\mathit{P}\left(\mathit{L}\right)}\ge \mathit{P}\left(\mathit{C}\right)$. Assuming that and then $\mathit{P}\left(\mathit{C}|\mathit{L}\right)>\mathit{P}\left(\mathit{C}\right)$. Observing that life exists definitely raises the ex ante probability that a creator exists for this world. Life is, in a sense, "evidence for" a creator.

However, to accept this argument as meaningful, we have to assume that . This assumption seems to require that we bite a serious philosophical bullet. If we take a frequentist ontology, then means that there exist possible worlds where no creator exists. This contradicts one theistic definition of God as a modally necessary being: if God exists, God exists in all possible worlds. In this case, $\mathit{P}\left(\mathit{C}\right)=1$, and $\mathit{P}\left(\mathit{C}|\mathit{L}\right)=1$; because we were already certain, by definition, that God existed. Under a Bayesian ontology, $\mathit{P}\left(\mathit{C}\right)$ represents our subjective confidence that God exists, and entails that we can reasonably be in doubt that God exists, which contradicts at least Plantinga's argument that God as properly basic: $\mathit{C}\Rightarrow \mathit{P}\left(\mathit{C}\right)=1$. Thus, if the FTA is rationally persuasive, then God must be neither modally necessary nor properly basic. But suppose we bite these philosophical bullets.

Another portion of the FTA is also valid: Assuming that , then : Observing that life exists definitely lowers the ex ante probability that no creator exists for this world.

But so what? We really want to know whether or not $\mathit{P}\left(\mathit{C}\right)>\mathit{P}\left(~\mathit{C}\right)$. The question is not whether observing life makes the race closer, we want to know if observing life changes the winner. We want to know if $\mathit{P}\left(\mathit{C}|\mathit{L}\right)>\mathit{P}\left(~\mathit{C}|\mathit{L}\right)$. Because we want to know if this particular inequality is true that we must condition on $\mathit{L}$. The FTA does not, however, help us answer this question. Regardless of how small $\mathit{P}\left(\mathit{L}|~\mathit{C}\right)$ is, we do not know whether or not it is less than $\mathit{P}\left(\mathit{C}\right)$, and the FTA requires that $\mathit{P}\left(\mathit{C}\right)>\mathit{P}\left(\mathit{L}|~\mathit{C}\right)$. If we simply assume that $\mathit{P}\left(\mathit{C}\right)>\mathit{P}\left(\mathit{L}|~\mathit{C}\right)$, then we can just as simply assume that (neither assumption entails a contradiction), so the FTA works only on an arbitrary choice of assumptions, which essentially begs the question. And, according to Ikeda and Jeffries, we have a plausible argument that , because . If we assume that $\mathit{P}\left(\mathit{F}|\mathit{C}\right)=1$, then $\mathit{P}\left(\mathit{F}|\mathit{C}\right)=\mathit{P}\left(\mathit{L}|\mathit{C}\right)$ and we're back where we started.