Begging the question is a fallacious form of arguing in which one assumes what one claims to be proving. An argument is a form of reasoning whereby one gives a reason or reasons in support of some claim. The reasons are called premises and the claim one tries to support with premises is called the conclusion. An argument is said to beg the question when its conclusion is assumed to be true by its premises and the premises are used to prove the conclusion. The classic and simplest form of this fallacy is called arguing in a circle. But begging the question can sometimes be a bit more complicated than just circular reasoning such as America is the greatest country in the world because there are no countries better than the U.S.A.
Before explaining the fallacy of 'begging the question' in more detail, let me try to explain the difference between warranted and unwarranted assumptions.
An assumption is a claim that is taken for granted, for which no proof is given or argument made. Every argument makes assumptions. It would be ridiculously tedious and unreasonable to require every assumption in every argument to be proven before proceeding. But it is not improper to require that the assumptions of an argument be warranted or, if not, stated as conditional or provisional.
A warranted assumption is an assumption that is either known to be true or is reasonable to accept without requiring an argument to support it. Since a good argument must be based on true or reasonable assumptions, it follows that arguments based upon false or questionable assumptions are not good arguments. A questionable assumption is one that is controversial and one for which there is no general consensus among the vast majority of those with the appropriate knowledge or experience. A claim does not become questionable just be you or anyone else questions it; otherwise all claims would be questionable. The contrary of a questionable assumption is not an unquestionable assumption. There truly are very few claims that are unquestionably true in the sense of not possibly being false.
Even if we find that we cannot accept the premises of an argument, we might still find the argument instructive. The argument may clarify concepts we are fuzzy on, or introduce new material we were ignorant of, or make us aware of material that should be included in an argument on the topic at hand. The argument may serve as a model of reasoning; for, the arguer whose premises we cannot accept might be very adept at drawing conclusions from those premises.
Finally, do not consider an assumption unwarranted simply because you do not know whether it is true. Your lack of knowledge does not make a claim questionable. Also, don't assume that just because consensus claims in science are questioned by some people that such questioning implies that the consensus claim is questionable. Just because, for example, some people believe that vaccines cause autism does not make the claim that vaccines don't cause autism a questionable claim.
The following argument begs the question.
We know a god exists because we can see the perfect order of creation, an order which demonstrates supernatural intelligence in its design.
The conclusion of this argument is that a god exists. The premise assumes a creator and designer of the universe exists, which many people would take to mean that a god exists. In this argument, the arguer should not be granted the assumption that the universe exhibits intelligent design, but should be made to provide support for that questionable claim.
The following argument also begs the question.
The conclusion of the argument is entailed in its premises. If one assumes that abortion is murder then it follows that abortion should be illegal because murder is illegal. Thus, the arguer is assuming abortion should be illegal (the conclusion) by assuming that it is murder. In this argument, the arguer should not be granted the assumption that abortion is murder, but should be made to provide support for this controversial claim.
The following is another example of begging the question.
Paranormal phenomena exist because I have had experiences that can only be described as paranormal.
The conclusion of this argument is that paranormal phenomena exist. The premise assumes that the arguer has had paranormal experiences, and therefore assumes that paranormal experiences exist. The arguer should not be granted the assumption that his experiences were paranormal, but should be made to provide support for this questionable claim.
Here is another example of begging the question.
Past-life memories of children prove that past lives exist because the children could have no other source for their memories besides having lived in the past.
The conclusion of this argument is that past lives exist. Claiming that the childrens' memories could have no other source than a past life is to assume that past lives exist. The arguer should not be granted the assumption that children have had past lives but should be made to support this questionable claim.
1) DNA is not merely a molecule with a pattern; it is a code ... and an information storage mechanism.
Marshall assumes what he should be proving, namely, that all codes are created by a conscious mind. Even if it is true that scientists have not found any natural process that creates coded information--something only one with specific knowledge of the science of natural processes and codes could know--it is still possible such processes exist. Here Marshall commits the fallacy of argument to ignorance. (He also claims that DNA is a language, which is arguable, and that no language has evolved naturally, another questionable claim.) The two premises in this argument are questionable for the same reason that the conclusion is questionable.
Note for the student of logic who knows about valid argument forms such as modus ponens: It has sometimes been said that in a sense, all deductively valid arguments beg the question. However, the above definition of begging the question--If one's premises entail one's conclusion, and one's premises are questionable, one is said to beg the question--distinguishes the two somewhat. In any case, modus ponens, for example, is always a valid form of arguing, even if its premises are false and even if it begs the question.
See also logical fallacies and Becoming a Critical Thinker, ch. 5.