As usual, be careful not to apply this principle selectively - your own in-series arguments need complete inspection to be accepted, and others' in-parallel arguments need complete inspection to be rejected.Ĭaveat: When I was getting feedback on this post, somebody pointed out that the presence of two bad examples actually can weaken the case made for the theory if your reasoning process involves evaluating how competent the person presenting it is. I thought it was cute, and maybe useful, so I decided to post it. I'm guessing most people who will read this post already understand what I'm saying, but I've never seen it presented with the 'in parallel' and 'in series' phrasing before. If the link from B to C is suspect, then the entire argument is suspect, even if the link from A to B is irrefutable. Somebody might begin with premise A, use it to draw intermediate conclusion B, and then use that to draw final conclusion C.

When arguments are delivered in series, their combined strength is no greater than the strength of the weakest link. In both cases, the situation should have at least as much 'persuasion power' as it would if the worse arguments did not exist. Or somebody might give five examples of a phenomenon they say exists, two of which are stretches but three of which work out all right. For example, you might encounter two different people arguing in favor of the same position, one giving an argument that you can easily see doesn't work, and one giving an argument that's harder to refute. When arguments are delivered in parallel, their combined strength is no less than the strength of the strongest argument.

Gish gallop example