Note: You might want to read How to Argue first, to understand the structure of arguments in general.
An argument from analogy is similar to what we simply call an analogy, but is different in that it’s an argument, whereas an analogy is usually just a stating of a similarity. “Your driving is like Rahul Dravid’s batting” – that’s an analogy (and a compliment I once received!). It’s simply saying A is like B. But an argument from analogy – henceforth referred to as an “AFA” – is an inductive argument, which states the existence of a further similarity as its conclusion. It takes the following form:
1. Object A has property P (and possibly Q, R…).
2. Object B also has property P (and Q, R…).
3. Object B has property X.
——————————————————
4. Object A also has property X. (From 1-3.)
Here’s an example which some of us might have experienced. Say I’m up for a promotion at work, and I think I’ll be promoted, but I’m not. And then I find out that my colleague has been promoted. So I go to my boss and I argue for my promotion by saying:
“You promoted <colleague>, why didn’t you promote me?”
I’ll try to reconstruct this AFA in the above form. First, what are the two objects being compared? Easy enough – me and my colleague. I.e.,
A = me
B = colleague
Next, what are the common properties P, Q, R and so on? It’s implicit that there must be some similarities between my colleague and I, so let’s say we both joined around the same time, and have similar experience levels:
P = 5 years of relevant experience
Q = joined the company in 2009
Finally, X is the property of being promoted:
X = got promoted
So as you can now see, the conclusion “A also has property X” is “I should also be promoted”.
When is an Argument From Analogy Strong?
An AFA is stronger when it has the following attributes:
- Many relevant similarities: the similarities P, Q, R… are relevant to X and many in number. The similarities I noted above are certainly relevant to the issue of promotion. But other similarities might not be relevant – e.g. if my colleague and I both have degrees in philosophy, but philosophy isn’t relevant to our job, then that similarity isn’t relevant to our promotion. But if my colleague and I both hit a particular sales target in the last quarter, and we both won a particular award… the more relevant similarities there are, the stronger the argument becomes.
- Fewer relevant differences: there are fewer relevant dissimilarities between A and B. What if it turns out that my colleague passed a well-regarded industrial certification, and I hadn’t? Or received previously-unheard of praise from the customers? Or won major new business? Or hired and coached a brilliant team? If I have done none of these things, then these differences are relevant, and they would weaken my argument.
- Diverse objects: there are other objects C, D, E… which also have similarities P, Q, R… and X. If I can identify three or four other colleagues who also share those similarities and got promoted, then my case for promotion becomes stronger.
- Weaker conclusion: If instead of saying “You definitely should have promoted me”, I say “You probably should have promoted me”, the argument becomes stronger. Granted, in this particular example it wouldn’t make much sense, since promotion is a yes-or-no state. But in general, the principle holds – a weaker conclusion has more support from the premises of an AFA.
Here’s a real-life AFA from a few days ago – in a Wall Street Journal interview, the CEO of American financial services firm AIG said this while responding to criticism of AIG executives receiving bonuses despite the company being in bad shape:
The uproar over bonuses was intended to stir public anger, to get everybody out there with their pitch forks and their hangman nooses, and all that–sort of like what we did in the Deep South [decades ago]. And I think it was just as bad and just as wrong.
He later apologised (kind of). Most of us can instinctively make out what’s wrong with this argument, but it helps to break it down into the above form, to see just why it’s a weak argument:
A = executives of AIG who received bonuses
B = African-Americans in slavery/civil rights era
P = demonised by media and public opinion
X = ought to be left in peace.
The argument appears to point out an additional similarity by use of the phrases pitchforks and hangman’s nooses, but for one object (A) these phrases are rhetorical, but for the second (B) they are literal (an equivocation fallacy perhaps?). So we’re left with that one similarity P, of questionable relevance, and of course there are a host of relevant dissimilarities between A and B. As a result, this is a very weak argument from analogy.
A more detailed and academic look at AFAs can be found at the Stanford Encyclopedia of Philosophy.
Sunil D'Monte 