Applied math

Recent statements by Whitehouse chief of staff John Kelly provide an interesting opportunity to learn about math. I’m thinking specifically about Kelly’s statement that we shouldn’t judge the opinion on slavery by Robert E. Lee through the lens of modern sensibilities.

Kelly’s argument, as I understand it, is that we shouldn’t be too harsh on Lee, because most people thought slavery was perfectly normal back in the early 1860’s. Therefore, he reasons, it is unfair to judge Lee by applying our 21st century values.

Let’s do some math. Suppose we say, to be generous, that 60% of white Americans were at the time in favor of slavery (the actual percentage was lower, but I’m being generous).

Now we know that in slave-holding regions of the U.S., roughly 40% of the population consisted of slaves. Let’s put these numbers together, with the reasonable assumption that slaves themselves were not in favor of slavery.

If 60% of 60% of a population is pro-slavery, that means that 36% that population is pro-slavery, which means that 64% is against slavery. That comes out to an overwhelm opinion against slavery: Nearly twice as many people are against slavery than are for it.

Unless you think that certain darker skinned members of the population were not “people”. Hmm.

Surely that’s not what Kelly is implying. Or is it?

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