Phil 148
Parallel Reasoning in Thomson’s “A
Defense of Abortion”
Parallel Reasoning
• Sometimes, when an argument is invalid or
otherwise problematic, it is easier to refute by
constructing a parallel argument that is more
clearly problematic.
• A parallel argument is one that retains the
same structure and other relevant features
but that is more clearly problematic than the
original.
Examples:
• From the text:
– “If I had a higher salary, I could buy more things; so if
everyone had higher salaries, everyone could buy more
things.” vs. “If one person stands up at a ballgame, he will
get a better view; so if everyone stands up at a ballgame,
everyone gets a better view”
– “If guns are outlawed, only outlaws will have guns” vs. “If
gum is outlawed, only outlaws will have gum.”
• Other:
– “The Heat have the best players, so they have the best
team” vs. “That is the most beautiful building on the block,
so it must have the most beautiful nails and rivets on the
block”
Evaluating Parallel Reasoning
1. Is the parallel argument actually
problematic? (i.e. are the parallel premises
true while the parallel conclusion is false?) If
not, then the refutation by parallel reasoning
is unsuccessful.
2. Does the parallel argument really have the
same form as the original? If not, then the
refutation by parallel reasoning is
unsuccessful.
Parallel Reasoning in Ethics
• Parallel reasoning in ethics can be a very
useful tool. When we encounter something
that we are unsure about ethically, what we
can do is see if it is relevantly similar to
something that we are sure about ethically.
– E.g. is downloading copyrighted electronic music
more like dipping a glass of water from a river that
you do not own or like taking someone else’s
property from their home?
• Parallel reasoning is one way to justify some
claims in ethics, so long as it is done well.
Thomson’s approach:
• Thomson’s approach is primarily defensive.
She does not mean to categorically support
any and all cases of abortion. Instead she
wishes to more closely examine common
assertions concerning positions that
categorically deny any and all cases of
abortion.
Notable features of both positions:
• “Personhood” will end up having nothing at all
to do with either essay’s conclusions (in fact,
Thomson assumes for the sake of argument
that a fetus is a person, while Marquis
assumes for the sake of argument that a fetus
is not a person)
• Religious reasoning makes no appearance
whatsoever.
The nature of rights
Rights are claims to some moral good, and as such
there are two kinds of rights:
- Positive: rights that put a definite claim onto
another person or entity (e.g. a right to education)
- Negative: rights that put a claim on all to refrain
from something (e.g. property rights)
It is not enough to simply claim that a person has a
right to something. One must defend the claim that
the right entails in order for the right to be justified.
Thompson on Rights
• Thompson explicitly addresses both forms of
the right to life, and addresses each in a
variety of ways.
• Each of the parallel arguments assumes one
version of the right to life or another.
Evaluating parallel reasoning in Thompson
• First, note that there are MANY parallel arguments in
Thompson, each with its own distinct purpose.
• Among these are:
– Violinist case (which has several scenarios, depending on
what is being addressed)
– Henry Fonda
– 2 boys with one coat
– 2 boys jointly given one box of chocolates
– Growing person in the house
– Burglar in the house
– People-seeds in the house
Violinist/Fonda Cases
• These cases all attempt to zero in on what
people owe to others in need, and to what
extent people are morally required to accept
sacrifices for the sake of those others.
2 Boys cases:
• These cases all concern ownership, and what
we do or do not owe others in need when
circumstances involve what is owned by one
party or another
House cases:
• These cases concern ownership and what
obligations that others owe to those who own
things, even when they need those things.
Evaluating parallel reasoning in Thompson
• Now, consider the specific cases.
• 1. Determine what claim Thompson is
meaning to establish/refute.
• 2. Determine whether the morally relevant
aspects of the parallel case match.
• 3. Determine whether the conclusion of the
parallel case is as Thompson indicates.