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Lecture 7

PHI 1101 Lecture Notes - Lecture 7: Eye Color, Intelligent Designer, Iced Tea

Course Code
PHI 1101
Mark Brown

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Chapter 7: Argument by Analogy
An analogy is a comparison of two or more things that are alike in specific ways.
‘Animals, like humans, have nerves, a spinal cord, and a brain. So, like humans,
animals must feel pain.’
‘Humans can move, do math, and fall in love. Robots can move, and do math. So,
robots can fall in love.’
Thing A has properties P1, P2, P3, and P4.
Thing B also has properties P1, P2, and P3.
Therefore, thing B likely has property P4.
Evaluating or Judging Arguments from Analogy
We need to consider:
Relevant similarities
Relevant dissimilarities
Number of instances compared
Diversity among cases
Relevant Similarities
The more relevant the similarities are between the things being compared, the
more probable the conclusion.

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‘Just like in Vietnam, the U.S. has not got the support of the international
community for its actions in Iraq. So, just like in Vietnam, the U.S. will
lose the war in Iraq.’
Appears weak, as there is just one similarity.
LOTS of other factors matter here.
Compare this:
‘Just like in Vietnam, the U.S. lacks the support of the international community,
and they lack an exit strategy, face a non-traditional enemy, and have lukewarm
support from the American people. So, just like in Vietnam, the U.S. will lose the
war in Iraq.’
Still not conclusive, but this argument from analogy is much stronger for
the reason that more similarities are provided.
Relevant Similarities are Important
However, it’s not the sheer number of similarities that matters.
How relevant or important those similarities are matters too.
If we’re comparing power of 2 armies ...
Number of soldiers, firepower, training, command
structure, etc. all matter.
Eye colour, astrological signs, music preferences, etc.,
Relevant Dissimilarities
The more relevant the dissimilarities between the two things compared, the less
probable the conclusion is.
For example, sometimes we point out key dissimilarities in order to
criticize someone’s argument by analogy.
‘Charcoal is like diamonds: they’re both 100 per cent carbon. So,
charcoal can cut glass.’
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