When somebody accuses another person of being inconsistent, not for an immediate lapse in logic, but for holding supposedly inconsistent beliefs in different situations, I think of Daniel Kahneman’s Thinking, Fast and Slow. On building coherent — internally consistent — stories, Kahneman writes,
The measure of success for System 1 is the coherence of the story it manages to create. The amount and quality of the data on which the story is based are largely irrelevant. When information is scarce, which is a common occurrence, System 1 operates as a machine for jumping to conclusions. Consider the following: “Will Mindik be a good leader? She is intelligence and strong…” An answer quickly came to your mind, and it was yes. You picked the best answer based on the very limited information available, but you jumped the gun. What if the next two adjectives were corrupt and cruel?
— p. 85.
The majority of us are probably not capable of building, in our head, a truly consistent and accurate model, or even a set of rules. Instead, we use abstractions and heuristics to help us associate different ideas. Using these heuristics, for example, we can decide whether some policy fits our worldview (e.g. whether a libertarian should support countercyclical monetary policy). But, these stories that we come up with to justify our decisions are necessarily based on limited information, so there is some probability that part of the story is wrong.
One problem is when we judge an idea on the basis of its consistency with an existing body of beliefs. Suppose that idea A is inconsistent with the rest of our body of beliefs. Should we reject idea A, on the basis of this inconsistency? It doesn’t make sense to me to keep the body fixed, but to vary the idea. I like to think about the process of critical analysis by imagining separate ideas as puzzle pieces. We’re interested in fitting them together, but none of the puzzle pieces are fixed — they are all allowed to vary. Thus, if I find that idea A is inconsistent with part of the rest of the puzzle, I don’t only vary idea A, I also vary the other pieces. I do this because I’m aware that, somewhere, I could have gone wrong when forming the rest of the puzzle, so the rest of it is as susceptible to the charge of inconsistency as idea A is.
Is consistency important: sure. Should it be a standard by which to judge independent ideas: I don’t think so.