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Adler: The Realm of Doubt
My students occasionally ask me epistemological questions, such as: "How do we know that we know what we know?" "What level of certainty do we need in order to believe something?" "What is the difference between knowledge and opinion?" and the like.
The clearest and most enlightening statement I have read about questions like this is from Mortimer J. Adler, in The Six Great Ideas (1981), pp. 45-55. Here is the relevant excerpt, without commentary.
The Realm of Doubt – Mortimer J. Adler - from Six Great Ideas (1981), chapter 7, pp.44-55
When should we say, “I know,” and do so with complete
assurance? When, after expressing a judgment, are we warranted in adding, “This
is something that I know beyond the shadow of a doubt”?
When instead, with something less than complete assurance
and yet not without some basis for our judgment, should we say, “I believe,” “I
think,” “I have the opinion that ...” or use such phrases as “in my judgment”
or “in my opinion”? When, after expressing a judgment, should we add the
comment: “This is something I have reason to believe is true”?
The criteria for drawing the line that divides the realm of
certitude from the realm of doubt can be stated abstractly. As so stated, the
criteria are not difficult to understand. Difficulties only arise when we try
to apply these criteria to particular cases in an attempt to decide which of
our judgments belong in the realm of certitude and which in the realm of doubt.
The criteria are as follows. A judgment belongs in the realm
of certitude when it is of the sort that (1) cannot be challenged by the
consideration of new evidence that results from additional or improved
observations, nor (2) can it be criticized by improved reasoning or the
detection of inadequacies or errors in the reasoning we have done. Beyond
challenge or criticism, such judgments are indubitable, or beyond doubt.
In contrast, a judgment is subject to doubt if there is any
possibility at all (1) of its being challenged in light of additional or more
accurate observations or (2) of its being criticized on the basis of more
cogent or more comprehensive reasoning.
Let me illustrate this by reference once again to judicial
proof in a jury trial of issues of fact. In criminal prosecutions, the degree
of proof required is defined as being “beyond a reasonable doubt.” But this
does not take the verdict rendered by the jury out of the realm of doubt.
What the jury is asking to bring in is a verdict that they
have no reason to doubt – no rational basis for doubting – in the light of all
the evidence offered and the arguments presented by opposing counsel.
It always remains possible that new evidence may be
forthcoming and, if that occurs, the case may be reopened and a new trial may
result in a different verdict. It also remains possible for the verdict to be
appealed to a higher court on the grounds of procedural errors that affected
the weighing of the evidence in the deliberations of the jury.
The original verdict may have been beyond a reasonable doubt
at the time it was made, but it is not indubitable – not beyond all doubt or
beyond the shadow of a doubt – precisely because it can be challenged by new
evidence or set aside by an appeal that calls attention to procedural errors
that may have invalidated the jury’s deliberations – the reasoning they did in
weighing and interpreting the evidence presented.
In civil litigation, the degree of proof required is defined
as being “by a preponderance of the evidence.” Here the jury’s verdict claims
no more than that the answer it gives to a question of fact has greater
probability than the opposite answer. As the jurors have interpreted and
weighed the evidence, they have found that it tends to favor one answer rather
than another. Here, as in a criminal prosecution, additional evidence or better
thinking on the jury’s part might result in a different verdict. The balance
might shift in the opposite direction.
In the affairs of daily life, many of the judgments we make
are, like jury verdicts, beyond a reasonable doubt or are favored by a
preponderance of the evidence. For all practical purposes, we regard judgments
of the first sort as being so highly probable that we act on them as if they
were certain. We need not hesitate to act on them even though new evidence may
be discovered. In the light of all the evidence we have before us and the
thinking we have done, we have no reason at present to doubt the truth of such
judgments. But we should always remember that that does not make them
indubitable; that does not give them the kind of certitude that removes them
from the realm of doubt.
The essential difference between genuine certitude and the
substitute for it that is often called “moral certainty” or “practical certainty”
lies in the finality and incorrigibility of indubitable judgments. Even when we
act on a highly probable judgment as if it were a certainty for all practical
purposes, it remains a judgment that is subject to correction, to challenge,
and to criticism. It is one about which we may in the future think it
reasonable to change our minds.
In a wide variety of daily affairs – in the conduct of
family life, in the care of our bodies and in all matters of health and
disease, in our business or professional careers, in our financial dealings,
especially in making investments, in our political discussions, especially with
regard to foreign policy and internal relations – we frequently act on
judgments that are not beyond a reasonable doubt, but are simply more probable
than their opposites. In the light of the evidence available at the time and in
the light of the best thinking we have done so far, we regard them as more
likely to be true.
The critical caution we must exercise is contained in the
words “at the time” and “so far.” These words remind us that the future always
holds the possibility of additional evidence and better thinking, either of
which may shift the weight of probability in the opposite direction.
The realm of doubt is the realm of judgments that have a
future, for better or for worse. This is not so in the case of judgments that
have the finality and incorrigibility of certitude.
If we turn now from judgments that we make in the practical
affairs of daily life to the conclusions of historical research, to the
findings, hypotheses, and theories of the investigative sciences, and even to
certain branches of mathematics, the same criteria function to place in the
realm of doubt a fairly large portion of what these learned disciplines offer
us as knowledge. This assessment may appear shocking to those who,
distinguishing between knowledge on the one hand and opinion or belief on the
other hand, regard history, science, and mathematics as branches of organized
knowledge, not as collections of mere opinions or beliefs.
The word “knowledge” for them has the connotation of truth;
in fact, it is inseparable from it. There cannot be false knowledge, as there
can be false opinions and beliefs. The phrase “true knowledge” is redundant;
the phrase “false knowledge” is self-contradictory.
However, those who hold this view acknowledge that there is
progress in these disciplines. They as well as everyone else speak of the
advancement of learning in all these fields. They attribute it to new discoveries,
improved observations, the development of sounder hypotheses, the substitution
of more comprehensive theories for less comprehensive ones, more elaborate and
more precise analysis or interpretation of the data at hand, and rectified or
more rigorous reasoning. Less adequate formulations are replaced by better ones
– better because they are thought more likely to be true, or nearer to the
truth being sought and, therefore, better approximations of it.
In short, all these branches of organized knowledge have a
future, a future they would not have if the present found them in possession of
judgments about what is true or false that had finality and incorrigibility. To
whatever extent history, science, and mathematics have a future, to that same
extent these bodies of “knowledge” belong in the realm of doubt, not in the
realm of certitude.
I put the word “knowledge in quotation marks because the
word has two meanings, not one. The same holds for the word “opinion.” The
recognition of the two senses in which we use these words will overcome the
shock initially experienced by those who recoiled from locating history,
science, and mathematics in the realm of doubt, because they are accustomed to
regarding them as branches of knowledge, not as collections of opinions or
beliefs.
Let us first consider the meaning of the word “knowledge”
that has already been mentioned. It is the sense in which knowledge cannot be
false and, therefore, has the infallibility, finality, and incorrigibility that
are attributes of judgments in the realm of certitude. Let us call this the
strong sense of the term.
At the opposite extreme from knowledge in this strong sense
is opinion in the weak sense of that term. When we use the word “opinion” in
this sense, we refer to judgments on our part that are no more than personal
predilections or prejudices. We have no basis for them, either empirical or
rational. We cannot support them by appeal to carefully accumulated evidence or
by appeal to reasoning that gives them credibility. We do not, in short, have
sufficient reason for claiming that they are more likely to be true than are
their opposites.
We prefer the opinions to which we are attached on
emotional, not rational, grounds. Our attachment to them is arbitrary and
voluntary – an act of will on our part, whatever its causes may be. Since we
may just as capriciously adopt the opposite view, unfounded opinions of this
sort fall to the lowest level of the realm of doubt.
In between these two extremes lie judgments that can be called
knowledge in the weak sense of that term and opinion in the strong sense of
that term. Here we have judgments that are neither arbitrary or voluntary,
judgments we have rational grounds for adopting, judgments the probability of
which we can appraise in the light of all the evidence available at the moment
and in the light of the best thinking we can do – the best analysis and
interpretation we can make of that evidence, again at the moment.
At the moment! The future holds in store the
possibility of additional or improved evidence and amplified or rectified
reasoning. That fact, as we have seen, places such judgments in the realm of
doubt. They have the aspect of opinion because they may turn out to be false
rather than true, but they also have the aspect of knowledge because, at the
moment, we have no reason to doubt them. They are beyond reasonable doubt,
but not beyond the shadow of a doubt, from which they cannot escape because
they have a future.
Readers who have followed the argument so far may begin to
wonder whether the realm of certitude is a completely empty domain. If not,
what sort of judgment can we expect to find there?
The answer I am about to give applies not only to judgments
we make in the course of our daily lives, judgments ordinarily made by persons
of common sense, even the judgments such persons may come to make when their
common sense is enlightened by philosophical reflection. It also applies to
judgments in the field of mathematics and in some, if not all, of the empirical
sciences.
Truths called self-evident provide the most obvious examples
of knowledge in the strong sense of that term. They are called self-evident
because our affirmation of them does not depend on evidence marshaled in
support of them nor upon reasoning designed to show that they are conclusions
validly reached by inference. We recognize their truth immediately or directly
from our understanding of what they assert. We are convinced – convinced, not
persuaded – of their truth because we find it impossible to think the opposite
of what they assert. We are in no sense free to think the opposite.
Self-evident truths are not tautologies, trifling and
uninstructive, such as the statement “All triangles have three sides.” A
triangle being defined as a three-sided figure, we learn nothing from that
statement. Contrast it with the statement, “No triangle has any diagonals,”
which is both self-evident and instructive, not a tautology.
The self-evidence of the truth of the latter statement
derives immediately from our understanding of the definition of a triangle as a
three-sided figure and from our understanding of the definition of a diagonal
as a straight line drawn between two nonadjacent angles. Seeing at once that a
triangle contains no nonadjacent angles, we see at once that no diagonals can
be drawn in a triangle.
Our understanding of diagonals also enables us to see at
once that the number of diagonals that can be drawn in a plane figure that is a
regular polygon having n sides (where n stands for any whole
number) is the number of sides multiplied by three less than that number, the
product being then divided by two.
Sometimes, as in the case of “No triangle has any
diagonals,” the self-evidence of the truth derives from our understanding of
definitions. Sometimes, it derives from our understanding of the terms that are
not only undefined but are also indefinable, such as “part” and “whole.”
Since we cannot understand what a part is without reference
to a whole, or understand what a whole is without reference to parts, we cannot
define parts and wholes. Nevertheless, our understanding of parts and wholes
makes it impossible for us to think that, in the case of a physical body, its
parts are greater than the whole. That the whole body is always greater than
any of its parts is not only true, but self-evident.
Equally self-evident is the truth that nothing can both
exist and not exist at the same time; or that, at a given time, it can both
have and not have certain characteristics. Our understanding of what it means
for anything to act on another or be acted upon gives us another self-evident
truth. Only that which actually exists can act upon another and that other can
be acted upon only if it also actually exists. A merely possible shower of rain
cannot drench anyone; nor can I be protected from the rain by merely a possible
umbrella.
How about the prime example of self-evident truth proposed
in the Declaration of Independence – that all men are created equal? Clearly,
it is not self-evident as stated if the word “created” is understood to mean created
by God, for the existence of God and God’s act of creation require the
support of reasoning – reasoning that can be challenged. Suppose, however, that
the proposition had been “All men are by nature equal.” On what understanding
of the terms involved might that statement be regarded as self-evidently true?
First of all, we do understand “equal” to mean “neither more
nor less.” If, then, we understand “all men by nature” to mean “all human
beings” or “all members of the same species,” it becomes self-evidently true
for us that all are equal, which is to say that no human being is more or less
human than any other.
All persons have, in some degree, whatever properties belong
to all members of the species Homo sapiens. The inequality of one
individual with another lies in the degree to which this or that specific
property is possessed, but not in the degree of humanity that is common to all.
I have dwelled at some length on this example not only because
we will have to return to it in later chapters dealing with the idea of
equality, but also because the proposition about the equality of all human
beings may have to be defended against those who advance the opposite view –
Aristotle, for example, who maintains that some human beings are by nature born
to be free, and some are by nature born to be slaves; or the male chauvinists
over centuries past, and even in the present, who believe that females are
inferior human beings.
I think the truth of the proposition about human equality
can be defended against all these errors, but a self-evident truth should need
no defense whatsoever. Hence the proposition, though true, may not be a good
example of self-evident truth.
Another whole class of truths for which certitude may be
claimed consists of those called evident, rather than self-evident. I do not,
as Descartes thought, have to infer my existence from the fact that I am aware
of myself thinking. I perceive it directly, just as I perceive directly the
existence of all the physical objects that surround me. If there is any doubt
at all about the truth of such judgments, it is the merest shadow of doubt
about whether I am suffering a hallucination rather than actually perceiving.
When I am perceiving, not hallucinating, there can be no
doubt that the objects I am perceiving actually exist. Such judgments have a
semblance of certitude that falls short of complete certitude only to the
extent that a shadow of a doubt remains concerning the normality of my
perceptual processes.
Whether my perceptual objects exist when I am not perceiving
them is another question, to which I think the true answer is that they do, but
its truth is neither self-evident nor evident. Reasoning and argument are
required to defend its truth. If we go beyond judgments about the present
existence of objects that we are at the moment perceiving to judgments about
their existence at other times and placements, or to judgments about their
characteristics or attributes, we pass from the realm of certitude to that of
doubt. Though we less frequently misperceive than we misremember, our
perceptions as well as our memories give rise to judgments that are often in
error or otherwise at fault.
Judgments that articulate what we perceive or remember take
the form of statements about particulars – this one thing or that, one event
rather than another. We are also prone to generalize on the basis of our
perceptual experience. In fact, the judgments we are most likely to be
insistent about are generalizations from experience. Many of these are
unguarded and turn out to be unwarranted because we have said “all” when we
should have said “some.” Even scientific generalizations sometimes overstate
the case. The history of science contains many examples of generalizations that
have been falsified by the discovery of one or more negative instances.
The falsification that I have just referred to provides us
with one or more example of judgments that belong in the sphere of certitude.
When the discovery of a single black swan falsifies the generalization that all
swans are white, our judgment that that generalization is false is knowledge in
the strong sense of the term – final, infallible, incorrigible. Nothing that
might possibly ever happen in the future could reverse the judgment and make it
true rather than false that all swans are white.
The number of self-evident truths is very small. The number
of falsified generalizations, both those made by scientists and those made by
laymen, is considerable; and the number of perceptual judgments about the
evident truth of which we have certitude is very large. But it is not the
number that matters when we compare the realm of certitude with the realm of
doubt. What matters is that only judgments in the realm of doubt have a future,
a future in which the effort we expend in the pursuit of truth may bring us
closer to it.
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