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Shifting the Burden of Proof: Fallacies

As mentioned before, it is incumbent upon the writer to provide evidence or support for her position. To imply that a position is true merely because no one has disproved it is to shift the burden of proof to others.



Since no one has been able to prove God’s existence, there must not be a God.

There are two major weaknesses in this argument. First, the fact that God’s existence has yet to be proven does not preclude any future proof of existence. Second, if there is a God, one would expect that his existence is independent of any proof by man.

Reasoning by shifting the burden of proof is not always fallacious. In fact, our legal system is predicated on this method of thought. The defendant is assumed innocent until proven guilty. This assumption shifts the onus of proof to the state. Science can also validly use this method of thought to better understand the world—so long as it is not used to claim “truth.” Consider the following argument: “The multitude of theories about our world have failed to codify and predict its behavior as well as Einstein’s theory of relativity. Therefore, our world is probably Einsteinian.” This argument is strong so long as it is qualified with “probably”—otherwise it is fallacious: someone may yet create a better theory of our world.



Astronomers have created a mathematical model for determining whether life exists outside our solar system. It is based on the assumption that life as we know it can exist only on a planet such as our own, and that our sun, which has nine planets circling it, is the kind of star commonly found throughout the universe. Hence it is projected that there are billions of planets with conditions similar to our own. So astronomers have concluded that it is highly probable, if not virtually certain, that life exists outside our solar system. Yet there has never been detected so much as one planet beyond our solar system. Hence life exists only on planet Earth.


Which one of the following would most weaken the above argument?

  1. Thousands of responsible people, people with reputations in the community to protect, have claimed to have seen UFOs. Statistically, it is virtually impossible for this many people to be mistaken or to be lying.
  2. Recently it has been discovered that Mars has water, and its equatorial region has temperatures in the same range as that of northern Europe. So there may be life on Mars.
  3. Only one percent of the stars in the universe are like our sun.
  4. The technology needed to detect planets outside our solar system has not yet been developed.
  5. Even if all the elements for life as we know it are present, the probability that life would spontaneously generate is infinitesimal.

This argument implies that since no planet has been discovered outside our solar system, none exist and therefore no life exists elsewhere in the universe. Hence the burden of proof is shifted from the arguer to the astronomers.


Although choice (A) weakens the argument, it has a flaw: the UFOs may not be life forms.
Choice (B) is irrelevant. Although the argument states that the only life in the universe is on Earth, it is essentially about the possibility of life beyond our solar system.
Choice (C) also weakens the argument. However, one percent of billions is still a significant number, and it is not clear whether one percent should be considered “common.” Now, the underlying premise of the argument is that since no other planets have been detected, no others exist.
Choice (D) attacks this premise directly by stating that no planets outside our solar system have been discovered because we don’t yet have the ability to detect them. This is probably the best answer, but we must check all the choices.
Choice (E) strengthens the argument by implying that even if there were other planets it would be extremely unlikely that they would contain life.
The answer, therefore, is (D).


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