Premises, Conclusions, and Support

An argument is a series of statements used to persuade someone of something. That "something" is called the conclusion or main claim. The first job in analyzing any argument is to identify its conclusion. One way to identify conclusions, or other parts of an argument, is to look for their indicators.

Premises are statements that directly support the conclusion. A simple argument has two premises and a conclusion; a more complex argument may contain many claims, but these can always be divided up into groups of three--two premises and a conclusion. In an argument, the conclusion is only supported by its two premises, but each premise itself can be supported in a number of ways:

  • Supporting arguments. A supporting argument is one which has as its conclusion the same statement as the premise being supported. All premises can be supported in this way, but such supporting arguments are often not stated. A special type of supporting argument is a definition, and while these, too, are usually unstated, at times it is necessary to define a term because either the term itself or the particular denotation being used is unusual.
  • Assumptions. Eventually, all support for premises can be traced back to a set of beliefs which the person making the argument considers to be self-evident, and therefore not in need of further support or analysis. These may be called assumptions, presumptions, suppositions, or, in certain situations, postulates and axioms. Such assumptions serve as the premises for supporting arguments and, in general, any premise can be called an assumption.
  • Evidence. A premise can be made more acceptable when it supported by various kinds of evidence: statistical studies, historical information, physical evidence, observations, or experiments, eyewitness accounts, and so on. The relative strength of evidence is determined by how reliable a person believes it to be. Almost no evidence is beyond dispute--we might challenge the methodology of a study, the accuracy of the information, the manner in which physical evidence was collected, and the eyesight or motivation of an eyewitness. And remember that the evidence only supports the premises--evidence cannot be an argument itself.
  • Authority. Sometimes, we are not in a position to judge supporting evidence for ourselves: there may simply be too much of it, or it may be too technical in nature, or it may not be directly available to us. In those cases we often rely on the judgments of others, authorities whom we believe to be more likely to come to an accurate evaluation of the evidence than we are ourselves. Though we tend to think of such expertise in scientific, medical, or other scholarly fields, authority in arguments can also come from religious teachings, folk wisdom, and popular sayings--anything or anyone that we accept as somehow able to reach a more accurate evaluation. The relative strength of an authority in an argument depends on how willing a person is to accept the judgment of that source, but even in the strongest of cases, use of an authority merely supports a premise, and does not make an argument by itself.
  • Explanations and anecdotes. Sometimes, we are more willing to accept a premise if we are given background information or specific examples. Such explanations and accounts are not given the importance of evidence or authority in an argument. Anecdotal evidence, for example, is by definition less statistically reliable than other sorts of evidence, and explanations do not carry the weight of authority. But both anecdotal evidence and explanations may affect our understanding of a premise, and therefore influence our judgment. The relative strength of an explanation or an anecdote is usually a function of its clarity and applicability to the premise it is supporting.
The various sorts of support for a premise--supporting arguments, evidence, authority, and explanations and anecdotes--interact in what we might call a hierarchy of support or evidence, in which one sort is given priority over another. In a murder trial, for example, the prosecution is usually based on the assumption that the jury's hierarchy of evidence will have at the top physical evidence (fingerprints, blood samples), especially as explained by technical authorities (forensic pathologists, ballistics experts), followed by eyewitness accounts, then by other sorts of authorities (psychologists, sociologists), and finally by explanations and anecdotes (character witnesses, personal histories). If the prosecution is right, their strong physical evidence and eyewitness accounts will outweigh the defendant's character witnesses, because of their relative placement in the jury's hierarchy of evidence. However, because that hierarchy is determined by each individual on a case-by-case basis, one can never be totally sure how any one piece of support will be accepted.

Facts and Opinions. In the section on statements, we distinguish between three kinds of claims: verifiable, evaluative, and advocatory. Generally speaking, evidence takes the form of a verifiable statement, and authority takes the form of a evaluative statement. We have avoided using the terms "fact" and "opinion," in part because of the strong connotations these words carry. People tend to think that "facts" are much more reliable and convincing than "opinions," yet many "facts," such as statistical surveys, scientific measurements, and historical events, are ultimately based on "opinions." Thus, the difference between verifiable evidence ("The victim's blood was found on the suspect's clothes") and evaluative authority ("According to my analysis, the sample taken from the suspect's clothes matches the victim's blood type), is often more a matter of presentation than of fact vs. opinion.

Exercises

1. In each argument, there can be only one . . .

premise.

conclusion.

assumption.

statement.

2. What is the difference between anecdotal and other sorts of evidence?

Evidence should be factual, and an anecdote is not.

Evidence should be verifiable, and an anecdote is not.

Evidence should be statistically reliable, and an anecdote is not.

Evidence should be beyond dispute, and an anecdote is not.

3. In a murder trial, which of the following would usually be placed lowest in the hierarchy of evidence?

Fingerprints on the murder weapon.

An eyewitness account of the crime.

The defendant's prior criminal record.

A psychiatrist's report on the defendant's ability to tell right from wrong.

1. In each argument, there can be only one . . .

You answered:

premise.

Every argument has exactly two premises, though at times only one is stated, and at other times a complex argument may seem to have more than two.

1. In each argument, there can be only one . . .

You answered:

conclusion.

Correct!

Each argument can have only one conclusion, but that conclusion may be complex. In other words, "The United States is in North American, and infections can be treated by antibiotics, and tickets to the Pearl Jam concert will not be sold through Ticketmaster" could be the conclusion to a single argument, though encountering such an argument except as a critical thinking example would be unlikely.

1. In each argument, there can be only one . . .

You answered:

assumption.

Assumptions are either the premises of an argument, or the premises of that argument's supporting arguments. As a result, no argument has fewer than two assumptions, and most have many more than two.

1. In each argument, there can be only one . . .

You answered:

statement.

There are three statements (or claims) for every argument: two are premises and the third is the conclusion.

2. What is the difference between anecdotal and other sorts of evidence? You answered:

Evidence should be factual, and an anecdote is not.

We are not using the term "factual" in Mission: Critical, because it carries misleading connotations. If by "factual" you mean "true," in the sense of "verifiable," then it is quite possible for an anecdote to be verified. "There has been an increase in drivers running red lights in Santa Cruz this year," could be evidence, and "I've seen more drivers running red lights in Santa Cruz this year" could be anecdotal evidence. Both statements can be verified, at least in theory.

2. What is the difference between anecdotal and other sorts of evidence? You answered:

Evidence should be verifiable, and an anecdote is not.

It's true that evidence usually takes the form of a verifiable claim, but so can an anecdote. "There has been an increase in drivers running red lights in Santa Cruz this year," could be evidence, and "I've seen more drivers running red lights in Santa Cruz this year" could be anecdotal evidence. Both statements can be verified, at least in theory. Just because it would be difficult or impossible in practice to verify a claim does not change the type of claim it is in theory.

2. What is the difference between anecdotal and other sorts of evidence? You answered:

Evidence should be statistically reliable, and an anecdote is not.

Correct!

By definition, anecdotal evidence is gathered in an unscientific manner, usually based on someone's personal experiences. And while the anecdote may be true, there is no way to tell whether those personal experiences are common or very rare. Of course, bad evidence may not be statistically reliable, either, but it is presented as if it were.

2. What is the difference between anecdotal and other sorts of evidence? You answered:

Evidence should be beyond dispute, and an anecdote is not.

No evidence is beyond dispute, and an anecdote is probably no more likely to be disputed than any other kind of support. But anecdotal evidence, because it is usually based on limited, often personal experience, is subject to a different proportion of challenges than other kinds of evidence.

3. In a murder trial, which of the following would usually be placed lowest in the hierarchy of evidence? You answered:

Fingerprints on the murder weapon.

Physical evidence is often at the top of the hierarchy of support in a murder trial--even though we know that there can be errors in the gathering and interpretation of such evidence, as well as intentional falsification or "planting" of such evidence, either by the real perpetrator or by someone else with access to the crime scene or the evidence.

3. In a murder trial, which of the following would usually be placed lowest in the hierarchy of evidence? You answered:

An eyewitness account of the crime.

We all know that eyewitness accounts can be full of errors, since an eyewitness is only human. Still, an eyewitness account is usually given a high place in the hierarchy of evidence, depending on the perceived reliability of the individual.

3. In a murder trial, which of the following would usually be placed lowest in the hierarchy of evidence? You answered:

The defendant's prior criminal record.

Correct!

While a prior criminal record (or lack of one) may seem to tell a lot about the character of the defendant, it is usually inadmissable as evidence for the simple reason that the truth of the charges must be proven with evidence of that specific crime. The prior criminal record of a defendant (or the lack of one) is usually excluded as prejudical in determining guilt or innocence, although it is often considered in determining the sentence once an individual has been convicted of a crime.

3. In a murder trial, which of the following would usually be placed lowest in the hierarchy of evidence? You answered:

A psychiatrist's report on the defendant's ability to tell right from wrong.

In some ways, this would be highest in the evidence hierarchy, because if a defendant is unable to tell right from wrong, he or she usually must be acquitted for reasons of insanity. Even considering the defendant's mental capacity only at the time of the crime would present evidence directly related to the issue of guilt or innocence.

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