Therefore his brother sam is a democrat compare that

Therefore, his brother Sam is a Democrat.
Compare that argument with this one:
2.Both Bill and his brother Sam are attorneys and went to the same university. Bill is a Democrat.
Therefore Sam is a Democrat, too.
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Argument 2 is stronger than Argument 1, because it introduces two additional relevant similarities
between the premise analogue (Bill) and the conclusion analogue (Sam). Now look at Argument 3:
3.Bill is an attorney. His brother Sam is not. Bill went to Ohio State. Sam did not attend college. Bill is a
Democrat.
Therefore Sam is too.
Argument 3 is weaker than Arguments 1 and 2, because it introduces relevant differences between the
premise and conclusion analogues. Now look at Argument 4:
4.Bill has four brothers, including Sam. Bill and three of the brothers are Democrats.
Therefore Sam is a Democrat, too.
Argument 4 is just like Argument 1, but stronger, since it increases the number of brothers who are
Democrats. Next, look at Argument 5:
5.Bill has four brothers, including Sam. All the brothers including Sam are attorneys. Bill and three of the
brothers are Democrats.
Therefore Sam is a Democrat, too.
Argument 5 is even stronger than Argument 4. It references another attribute (being an attorney) shared
by all the brothers.

Here is Argument 6:
6.Bill, an attorney, has four brothers, including Sam. One of the other three sells real estate. Another is an
unemployed artist. The third owns a restaurant. These three and Bill are all Democrats.
Therefore Sam is a Democrat, too.
Actually Argument 6 is as strong as Argument 5, but for a different reason. We still have four premise-
analogues (Bill and the three brothers that don’t include Sam). Now it is true that, except for Bill, Sam’s
brothers aren’t attorneys. But in Argument 6 we don’t know what profession Sam is. The fact that Bill
and the other brothers are all Democrats despite exhibiting a diverse array of professions, makes it more
likely that, when it comes to this family, it doesn’t make any difference what Sam does professionally—
he is still apt to be a Democrat.
Guidelines for Thinking Critically About an Argument from Analogy
With these examples in mind, you can see that an argument from analogy can be evaluated using the
following guidelines:
■
The more similarities between the premise-analogue and the conclusion-analogue the stronger the
argument, and the fewer the similarities (or the more the dissimilarities) the weaker the argument.
■
Increasing the number of premise-analogues helps strengthen the argument, provided the
additional analogues are genuinely similar to the conclusion-analogue.
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■
Analogues that lack the attribute of interest are contrary analogues , and the fewer of them among
the premise-analogues the stronger the argument.