I was reading one of my favorite classic Logic texts, and I found a
great definition of a crucial principle of communication with others
(and self) called the "Law of Rationality."
When the book was written (more than 60 years ago), this principle was
so commonly adhered to; it is referred to as a "Law." Sadly, today,
adherence to this "law" has degenerated in many people's mind to
"Optional, to be followed only when I feel like it."
Luckily, most people enforce the following "Law of Rationality" when
dealing with other people about important issues in their lives. But,
unfortunately, often many people hold themselves to an opposite standard
when they are dealing with others.
Personally, I have found that the people I like and trust the most are
the people who, for the most part, adhere to the "Law of Rationality,"
both with regard to others, as well as with regard to themselves.
P.s., I provided one detailed explanation of one of the more common
evasions of the Law of Rationality, and a brief description of a couple
of others. (Unfortunately, there are countless ways to avoid being
rational, so if you would like a list of others, let me know.)
"The Law of Rationality and Evasions Thereof"
...An argument is a discourse containing inference, in which we say,
"This is so because of that." But the inference may be sound or
unsound. We will be concerned with the principles of sound reasoning.
Before proceeding to the principles, however, let us consider the aim of
logical thinking and the manner which this aim may be frustrated.
Every person who is interested in logical thinking accepts what we shall
call the "law of rationality," which maybe stated as follows: We ought
to justify our conclusions by adequate evidence.
The meaning of adequacy will be explained in detail as we proceed. Let
it suffice here to say that by "adequate evidence" we mean evidence
which is good and sufficient in terms of the kind of proof which is
required. There are occasions when we require conclusive proof, as in
mathematics, and there are occasions when it is sufficient to establish
the probability of a given conclusion, as in weather prediction. But in
all cases the evidence must be adequate to its purpose. ...
Though few, if any, will have the temerity or the foolishness to
challenge the law of rationality, it is often evaded. Evasion usually
occurs through carelessness, but it may also occur through design. In
this section we shall note some of the typical ways in which the
obligation to support beliefs by adequate evidence is evaded.
In every argument we find the assertion of a belief, which we shall call
"P," (for "probandum," or proposition to be proved). Someone says that
P is true. When we ask the speaker, "Why," or "What reasons do you have
for believing that P is true?" We ask for evidence. We then expect
adequate evidence to the question at issue, and it should be good and
sufficient evidence. In the rest of this chapter we shall be concerned
with the evasion of the requirement that evidence be furnished. The
proverb says that we ask for bread and were given stones. Paraphrased,
we shall find that we asked for evidence and received [, instead, some
form of a typical evasive pseudo-argument, such as the argument called,
"the appeal to authority," "the appeal to emotion," "the appeal to
ignorance," etc. etc.]
1. The Appeal to Authority
This evasion has the following structure: Jones says that P is true.
When asked, Why? He answers, "Because X says so." Now, P (the
probandum) should be proved by adequate evidence, but the fact that X
says it is true is not evidence for its truth. The citing of authority
in this bald manner is an evasion of the law of rationality.
Now, to say that "the appeal to authority" is an evasion of the law of
rationality is not to say that we are guilty of this evasion whenever we
cite an authority for our beliefs. There is no doubt that sensible
people must rely on authorities for many, if not most, of their
important decisions and for the beliefs on which these decisions are
When a physician tells us that we need an operation we relation his
authority. We accept the authority of the weatherman that rain is
probable. We have neither the time nor sufficient knowledge to
investigate the evidence for all our beliefs. The point, however, is
this: No belief is true merely because someone says so. It is true
because of the evidence in its behalf. When we trust an authority, we
merely place credence in the fact that he has evidence. And if we whish
to know, rather than merely to believe, we should inquire into the
evidence on which his conclusions are based. . . .
In general, three questions should be kept in mind when considering the
statements of an authority: Is the cited authority an authority in the
specific field in which he has made his pronouncements? Does the
authority have evidence to prove his statements? Do all qualified
investigations agree on the general soundness of the type of proof
offered? A great physicist may be an authority in the field of nuclear
physics, but that does not qualify him to be dogmatic in the field of
religion. A man may be very critical in one field and very uncritical
in another. ...[W]e accept the statements of astronomers that the mean
distance of the sun from the earth is close to 93 million miles, because
they are authorities with respect to such matters, their evidence is
available to all, and all qualified investigators agree on the soundness
of their methods. We accept our physician's statements that we should
take medicine for our ailments for similar reasons (or at least we
believe these reasons to hold). But even the acceptance of competent
authority is never a substitute for proof.
When the authorities are in conflict, i.e., when "the doctors disagree,"
tow courses of action are open to us. If the problem is a purely
theoretical one, and we are not required to take immediate action, we
should suspend judgment. If action is required, we should accept the
authority who appears to be most competent and trustworthy.
The appeal to authority is often call the "Argumentum Verecundiam," a
learned-sounding Latin phrase which means the "appeal to reverence." A
revered authority or tradition is often regarded as infallible, so that
anyone who disagrees is in some sense disloyal to that which out to be
revered. ...Reverence is not a substitute for evidential proof.
The fact that "everybody knows that this is so" is no proof. The masses
of men have frequently been mistaken. They once thought that the earth
was flat. They still believe that the speed of falling objects depends
on its weight. The voice of the people is not necessarily the voice of
God on all questions.
2. The Appeal to Emotion
The structure of this evasion: "The proposition 'P' is true."
Why?-Because I (or you) have strong feelings concerning it." But strong
feelings do not constitute evidence for the truth of a proposition.
The fact that people have emotional attachments to religious and
political doctrines does not make the doctrines true.
3. The Appeal to Ignorance
[The structure of this evasion:] "P is true." Why? "Because you can't
disprove it." This type of evasion often occurs in discussion which
involve religious faith. ... [The] inability to disprove is not
equivalent to proof. Only evidence gives us proof.
(L. Ruby, "Logic an introduction," 131)