Tag: Logic

Not All Good Arguments Are Logically Sound

Some interesting thoughts from James Gray on whether all good arguments are logically sound. Understanding why helps us appreciate good arguments.

Proof that not all arguments are logically sound
An argument against the belief that all good arguments are logically sound is the following:

  1. At least some good scientific theories were proven to be false.
  2. If at least some good scientific theories could proven to be false, then not all good arguments are logically sound.
  3. Therefore, not all good argument are logically sound.

Premise 1 – Is it true that “at least some good scientific theories were proven to be false?” Yes. For example, I think Newton’s theory of physics is a good example. It was believed that Newton’s theory of physics was complete and could predict any physical motion, but it failed to predict the motion of Mercury. However, Einstein’s theory of physics was able to predict the motion of Mercury and is now considered to be a better (and more complete) theory of physics.

Premise 2 – Is it true that “if at least some good scientific theories could proven to be false, then not all good arguments are logically sound?” Yes. Scientists give good arguments in favor of good scientific theories. If all good scientific theories are proven to be true by sound arguments, then they can’t be proven to be false. Sound arguments would guarantee the theories are true because the premises would be true and the arguments for the theories would be valid—valid arguments can’t have true premises and false conclusions at the same time.

Given these two premises, the conclusion must be true (that not all good arguments are logically sound). Why? Because this argument uses a valid logical form. The logical form is “a. If a, then b. Therefore, b.” This valid logical form is well-known to be valid and is called “modus ponens.”

Derek Parfit: Does Anything Matter?

I must admit that I have Derek Parfit‘s long-awaited book On What Matters sitting on my nightstand at the moment. I’m aided in my procrastination by its daunting length—over 1400 pages in two volumes.

Most of us might come to the same conclusion as Parfit on the question of what matters—”we rich people give up some of our luxuries, ceasing to overheat the Earth’s atmosphere, and taking care of this planet in other ways so that it continues to support intelligent life.”

What we gain from reading Parfait, however, according to the article below, “is the possibility of defending these and other moral claims as objective truths.”

If his new book is half as mind-blowing and lucid as Reasons and Persons, I’ll enjoy the moment I stop balking at its sheer intellectual size and immerse myself.

Many people assume that rationality is always instrumental: reason can tell us only how to get what we want, but our basic wants and desires are beyond the scope of reasoning. Not so, Parfit argues. Just as we can grasp the truth that 1 + 1 = 2, so we can see that I have a reason to avoid suffering agony at some future time, regardless of whether I now care about, or have desires about, whether I will suffer agony at that time. We can also have reasons (though not always conclusive reasons) to prevent others from suffering agony. Such self-evident normative truths provide the basis for Parfit’s defense of objectivity in ethics.

One major argument against objectivism in ethics is that people disagree deeply about right and wrong, and this disagreement extends to philosophers who cannot be accused of being ignorant or confused. If great thinkers like Immanuel Kant and Jeremy Bentham disagree about what we ought to do, can there really be an objectively true answer to that question?

Parfit’s response to this line of argument leads him to make a claim that is perhaps even bolder than his defense of objectivism in ethics. He considers three leading theories about what we ought to do – one deriving from Kant, one from the social-contract tradition of Hobbes, Locke, Rousseau, and the contemporary philosophers John Rawls and T.M. Scanlon, and one from Bentham’s utilitarianism – and argues that the Kantian and social-contract theories must be revised in order to be defensible.

Then he argues that these revised theories coincide with a particular form of consequentialism, which is a theory in the same broad family as utilitarianism. If Parfit is right, there is much less disagreement between apparently conflicting moral theories than we all thought. The defenders of each of these theories are, in Parfit’s vivid phrase, “climbing the same mountain on different sides.”

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You can buy the two-volume set or get the core of his argument in the first 400 pages of volume one. Parfit is also the author of the mind-blowing Reasons and Persons.