This isn't much more than a rotation (or maybe just a rephrasing), but:

When I offer a 10 second or less description of Effective Altruism, it is hard avoid making it sound platitudinous. Things like "using evidence and reason to do the most good", or "trying to find the best things to do, then doing them" are things I can imagine the typical person nodding along with, but then wondering what the fuss is about ("Sure, I'm also a fan of doing more good rather than less good - aren't we all?") I feel I need to elaborate with a distinctive example (e.g. "I left clinical practice because I did some amateur health econ on how much good a doctor does, and thought I could make a greater contribution elsewhere") for someone to get a good sense of what I am driving at.

I think a related problem is the 'thin' version of EA can seem slippery when engaging with those who object to it. "If indeed intervention Y was the best thing to do, we would of course support intervention Y" may (hopefully!) be true, but is seldom the heart of the issue. I take most common objections are not against the principle but the application (I also suspect this may inadvertently annoy an objector, given this reply can paint them as - bizarrely - 'preferring less good to more good'). 

My best try at what makes EA distinctive is a summary of what you spell out with spread, identifiability, etc: that there are very large returns to reason  for beneficence (maybe 'deliberation' instead of 'reason', or whatever).  I think the typical person does "use reason and evidence to do the most good", and can be said to be doing some sort of search for the best actions. I think the core of EA (at least the 'E' bit) is the appeal that people should do a lot more of this than they would otherwise - as, if they do, their beneficence would tend to accomplish much more.

Per OP, motivating this is easier said than done. The best case is for global health, as there is a lot more (common sense) evidence one can point to about some things being a lot better than others, and these object level matters a hypothetical interlocutor is fairly likely to accept also offers support for the 'returns to reason' story. For most other cause areas, the motivating reasons are typically controversial, and the (common sense) evidence is scant-to-absent. Perhaps the best moves are here would be pointing to these as salient considerations which plausibly could dramatically change ones priorities, and so exploring to uncover these is better than exploiting after more limited deliberation (but cf. cluelessness).

 

Interesting write-up, thanks. However, I don't think that's quite the right claim. You said:

The claim: If you want to contribute to the common good, it’s a mistake not to pursue the project of effective altruism.

But this claim isn't true. If I only want to make a contribution to the common good, but I'm not all fussed about doing more good rather than less, (given whatever resources I'm deploying) then I don't have any reason to pursue the project of effective altruism, which you say is searching for the actions that do the most good.

A true alternative to the claim would be:

New claim: if you want to contribute to the common good as much as possible, it's a mistake not the pursue the project of effective altruism.

But this claim is effectively a tautology, seeing as effective altruism is defined as searching for the actions that do the most good. (I suppose someone who thought how to do the most good was just totally obvious would see no reason to pursue the project of EA).

Maybe the claim of EA should emphasise the non-obvious of what doing the most good is. Something like:

If you want to have the biggest positive impact with your resources, it's a mistake just trust your instincts(/common sense?) about what to do rather than engage in the project of effective altruism: to thoroughly and carefully evaluate what does the most good.

This is an empirical claim, not a conceptual one, and its justification would seem to be the three main premises you give.

It seems to me there's a fourth key premise:

0. Comparability: It is possible to make meaningful comparisons between very different kinds of contributions to the common good.

Novelty: The high-impact actions we can find are not the same as what people who want to contribute to the common good typically do.

It's not entirely clear to me what this means (specifically what work the "can" is doing). 

If you mean that it could be the case that we find high impact actions which we not the same are what people who want to contribute to the good would typically do,  then I agree this seems plausible as a premise for engaging in the project of effective altruism.

If you mean that the premise is that we actually can find high impact actions which are not the same as what people who want to contribute to the common good typically do, then it's not so clear to me that this should be a premise in the argument for effective altruism. This sounds like we are assuming what the results of our effective altruist efforts to search for the actions that do the most to contribute to the common good (relative to their cost) will be: that the things we discover are high impact will be different from what people typically do. But, of course, it could turn out to be the case that actually the highest impact actions are those which people typically do (our investigations could turn out to vindicate common sense, after all), so it doesn't seem like this is something we should take as a premise for effective altruism. It also seems in tension with the idea (which I think is worth preserving) that effective altruism is a question (i.e. effective altruism itself doesn't assume that particular kinds of things are or are not high impact).

I assume, however, that you don't actually mean to state that effective altruists should assume this latter thing to be true or that one needs to assume this in order to support effective altruism. I'm presuming that you instead mean something like: this needs to be true for engaging in effective altruism to be successful/interesting/worthwhile. In line with this interpretation, you note in the interview something that I was going to raise as another objection: that if everyone were already acting in an effective altruist way, then it would be likely false that the high impact things we discover are different from those that people typically do.

If so, then it may not be false to say that "The high-impact actions we can find are not the same as what people who want to contribute to the common good typically do", but it seems bound to lead to confusion, with people misreading this as EAs assuming that he highest impact things are not what people typically do. It's also not clear that this premise needs to be true for the project of effective altruism to be worthwhile and, indeed, a thing people should do: it seems like it could be the case that people who want to contribute to the common good should engage in the project of effective altruism simply because it could be the case that the highest impact actions are not those which people would typically do.

"The greater the degree of spread, the more you’re giving up by not searching." This makes sense. But I don't think you have to agree with the "big" part of premise 1 to support and engage with the project of effective altruism, e.g. you could think that there are small differences but those differences are worth pursuing anyway. The "big" part seems like a common claim within effective altruism but not necessarily a core component?

(You didn't claim explicitly in the post above that you have to agree with the "big" part but I think it's implied? I also haven't listened to the episode yet.)

I define the ‘common good’ in the same way Will MacAskill defines the good in “The definition of effective altruism”, as what most increases welfare from an impartial perspective. This is only intended as a tentative and approximate definition, which might be revised.

I'm a bit confused by this, because "what most increases welfare" is describing an action, which seems like the wrong type of thing for "the common good" to be.  Do you instead mean that the common good is impartial welfare, or similar? This also seems more in line with Will.

One other quibble:

the search for the actions that do the most to contribute to the common good (relative to their cost).

I'm not sure we actually want "relative to their cost" here. On one hand, it might be the case that the actions which are most cost-effective at doing good actually do very little good, but are also very cheap (e.g. see this post by Hanson). Alternatively, maybe the most cost-effective actions are absurdly expensive, so that knowing what they are doesn't help us.

Rather, it seems better to just say "the search for the actions that do the most to contribute to the common good, given limited resources". Or even just leave implicit that there are resource constraints.