Evidence of absence - AbsoluteAstronomy.com

Evidence of absence is evidence

Evidence

Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...

of any kind that suggests (via certain types of inference

Contraposition

In traditional logic, contraposition is a form of immediate inference in which from a given proposition another is inferred having for its subject the contradictory of the original predicate, and in some cases involving a change of quality . For its symbolic expression in modern logic see the rule...

or deduction

Transposition (logic)

In the methods of deductive reasoning in classical logic, transposition is the rule of inference that permits one to infer from the truth of "A implies B" the truth of "Not-B implies not-A", and conversely. Its symbolic expression is:...

) the non-existence or non-presence of something. A simple example of evidence of absence: checking one's pocket for spare change and finding nothing but being confident that one would have found it if it were there. This is an example of modus tollens
Modus tollens
In classical logic, modus tollens has the following argument form:- Formal notation :...

, a type of logical argument.

In this regard Irving Copi

Irving Copi

Irving Marmer Copi was an American philosopher, logician, and university textbook author....

writes:

Of course, in practice, it can be difficult to agree whether a particular experiment was a sufficiently "qualified investigation".

Overview

The difference between evidence that something is absent (e.g. an observation that suggests there are no dragons) and a simple absence of evidence (e.g. no careful research has been done) can be nuanced. Indeed, scientists will often debate whether an experiment's result should be considered evidence of absence, or if it remains absence of evidence (e.g. the experiment could have missed what it was looking for).

The confusion is worsened since arguments from ignorance and incredulity

Argument from ignorance

Argument from ignorance, also known as argumentum ad ignorantiam or "appeal to ignorance" , is a fallacy in informal logic. It asserts that a proposition is true because it has not yet been proven false, it is "generally accepted"...

are often (wrongly) advanced in debates as proper "evidence of absence". A case in point: arguing "There is no evidence that this mysterious remedy does not work, therefore it works." Basically, this arguments from ignorance relies on a lack of research to somehow draw conclusions. While this is a powerful method of debate

Debate

Debate or debating is a method of interactive and representational argument. Debate is a broader form of argument than logical argument, which only examines consistency from axiom, and factual argument, which only examines what is or isn't the case or rhetoric which is a technique of persuasion...

to switch the burden of proof, appealing to ignorance is a fallacy

Fallacy

In logic and rhetoric, a fallacy is usually an incorrect argumentation in reasoning resulting in a misconception or presumption. By accident or design, fallacies may exploit emotional triggers in the listener or interlocutor , or take advantage of social relationships between people...

. Carl Sagan

Carl Sagan

Carl Edward Sagan was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books...

criticized such "impatience with ambiguity" using cosmologist Martin Rees' maxim, "Absence of evidence is not evidence of absence."

Of course, in carefully designed scientific

Science

Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

experiments, even null result

Null result

In science, a null result is a result without the expected content: that is, the proposed result is absent. It is an experimental outcome which does not show an otherwise expected effect. This does not imply a result of zero or nothing, simply a result that does not support the hypothesis...

s can be evidence of absence. For instance, a hypothesis may be falsified

Falsifiability

Falsifiability or refutability of an assertion, hypothesis or theory is the logical possibility that it can be contradicted by an observation or the outcome of a physical experiment...

if a vital predicted observation is not found empirically

Empiricism

Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

. At this point, the underlying hypothesis

Hypothesis

A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...

will be rejected or revised, or even rarely add ad hoc explanations

Ad hoc hypothesis

In science and philosophy, an ad hoc hypothesis is a hypothesis added to a theory in order to save it from being falsified. Ad hoc hypothesizing is compensating for anomalies not anticipated by the theory in its unmodified form....

. Whether the scientific community

Scientific community

The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

will accept a null result as evidence of absence depends on many things, including the detection power

Statistical power

The power of a statistical test is the probability that the test will reject the null hypothesis when the null hypothesis is actually false . The power is in general a function of the possible distributions, often determined by a parameter, under the alternative hypothesis...

of the applied methods, and the confidence

Confidence interval

In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...

of the inference.

Philosophic arguments that depend on evidence of absence are commonly referred to in peer-reviewed literature as "noseeum arguments". The argument form is specifically inductive

Inductive reasoning

Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

in that evidence is accumulated; as one collects a larger dataset the argument grows stronger. Some noseeum arguments are very strong, such as checking the fridge for milk and determining that there is none, since it is relatively easy to systematically remove every item from the fridge, verify that it is not milk, and visually inspect the empty space left over. At the other extreme are noseeum arguments about the existence, or lack thereof, of alien lifeforms. Since the universe is enormous relative to our known area, a noseeum argument stating that there are no alien lifeforms would be very weak.

Evidence vs. proof

Philosopher Steven Hales describes how there is widespread agreement that, as far as humans can be concerned, it seems that any inference

Inference

Inference is the act or process of deriving logical conclusions from premises known or assumed to be true. The conclusion drawn is also called an idiomatic. The laws of valid inference are studied in the field of logic.Human inference Inference is the act or process of deriving logical conclusions...

is fallible

Fallibilism

Fallibilism is the philosophical principle that human beings could be wrong about their beliefs, expectations, or their understanding of the world...

. Neither a negative claim, nor a positive claim, is ever absolutely certain (i.e. absolutely "proving" facts about reality seems impossible). For instance, someone who believes that they have seen Santa Claus may have been hallucinating, or otherwise deceived.

Philosophers acknowledge what is called the problem of induction

Problem of induction

The problem of induction is the philosophical question of whether inductive reasoning leads to knowledge. That is, what is the justification for either:...

, the idea that you never know when new information will prove you were wrong after all. Since inference in general is never certain, it may be more appropriate to say "you can't prove anything, strictly speaking (a negative or a positive)". Hales also worries that people often appeal to the problem of induction in order to continue believing in less justified beliefs (i.e. pseudoscience

Pseudoscience

Pseudoscience is a claim, belief, or practice which is presented as scientific, but which does not adhere to a valid scientific method, lacks supporting evidence or plausibility, cannot be reliably tested, or otherwise lacks scientific status...

"You can't prove a negative"

Notable skeptic James Randi

James Randi

James Randi is a Canadian-American stage magician and scientific skeptic best known as a challenger of paranormal claims and pseudoscience. Randi is the founder of the James Randi Educational Foundation...

sometimes uses the catchphrase "you can't prove a negative". He uses the example of looking for Santa Claus

Santa Claus

Santa Claus is a folklore figure in various cultures who distributes gifts to children, normally on Christmas Eve. Each name is a variation of Saint Nicholas, but refers to Santa Claus...

as an unprovable negative. A claim by philosopher Steven Hales is that no logician actually believes this, and the rule is an oversimplification. As explained above, depending on circumstances, one can be just as confident about a negative as a positive.
Hales points out that the second law of thought

Law of thought

The laws of thought are fundamental axiomatic rules upon which rational discourse itself is based. The rules have a long tradition in the history of philosophy. They are laws that guide and underlie everyone's thinking, thoughts, expressions, discussions, etc.The three classic laws of thought are...

is a sort of negative; "it is not the case that a thing can be X and not X at the same time". What's more, any argument can be expressed in its negative form. For example, to the extent that you can prove that you are real (a positive argument), you can also prove that you are not imaginary. Whether an argument is phrased as a positive or negative can be arbitrary.

Hales acknowledges that people may actually mean "you can't prove that something doesn't exist". This claim is now clearer as an argument that "noseeum" arguments about the universe tend to be very weak as explained above. But it remains false as far as it concerns issues of "proof" and certainty

Certainty

Certainty can be defined as either:# perfect knowledge that has total security from error, or# the mental state of being without doubtObjectively defined, certainty is total continuity and validity of all foundational inquiry, to the highest degree of precision. Something is certain only if no...

in general as described in the previous section.

Existence of God

Whether humans possess evidence of absence for the existence of God continues to be debated

Existence of God

Arguments for and against the existence of God have been proposed by philosophers, theologians, scientists, and others. In philosophical terms, arguments for and against the existence of God involve primarily the sub-disciplines of epistemology and ontology , but also of the theory of value, since...

in philosophical academia. Research into the relationship between science and religion has also yielded mixed opinions.

British philosopher Antony Flew

Antony Flew

Antony Garrard Newton Flew was a British philosopher. Belonging to the analytic and evidentialist schools of thought, he was notable for his works on the philosophy of religion....

holds that some claims cannot be falsified because they are ultimately unverifiable. Flew asserts that one should test whether a certain truth claim can be falsified under a hypothetical situation. He suggests we ask "What would have to occur or to have occurred to constitute for you a disproof of the love of, or the existence of, God?" Flew also describes how deep questioning, backed up by empirical testing, can reveal a claim to at least have much less content than was originally thought (e.g. it becomes a much less detailed claim)- what he calls "death by a thousand qualifications

Ad hoc hypothesis

".

God's existence can mean many things to many different people. Still, some claims (which are actually contentful) about gods or their actions can be falsified, to the extent that the claims attempt to describe any facts about physical reality. For instance, the creationist claim that God created humankind in their current form has been falsified by evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

. Many (but certainly not all) other claims related to God can be similarly tested (e.g. the practice of praying to cause someone to heal

Faith healing

Faith healing is healing through spiritual means. The healing of a person is brought about by religious faith through prayer and/or rituals that, according to adherents, stimulate a divine presence and power toward correcting disease and disability. Belief in divine intervention in illness or...

has also been recognized, among scientists, as having been disproved).

Other examples

Some other instances of evidence of a thing's absence include: A biopsy may show the absence of malignant cells (evidence of absence of a tumour), and the result of Michelson–Morley experiment is interpreted as "strong evidence" that the luminiferous aether

Luminiferous aether

In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light....

does not exist. Another case in point, close inspection of an attic may reveal no sign of vermin infestation and therefore evidence of vermin absence in the attic. Note however that a critic might argue, if one did not open every available box, that one still possesses an absence of evidence.

In the media

Gin Rummy, an ex-soldier character in the show The Boondocks

The Boondocks

The Boondocks was a daily syndicated comic strip written and originally drawn by Aaron McGruder that ran from 1996 to 2006. Created by McGruder in 1996 for The Diamondback, the student newspaper at the University of Maryland, College Park, the strip moved from the college pages and was printed in...

, attempts to explain to another character what it means to say "the evidence of absence is not the absence of evidence". As Rummy puts it "Simply because you don't have evidence that something does exist does not mean you have evidence that something doesn't exist." When that rephrasing causes confusion, Rummy angrily discusses more confusing but related ideas, saying: "Well, what I'm saying is that there are known knowns and that there are known unknowns. But there are also unknown unknowns; things we don't know that we don't know."

Overview

Evidence vs. proof

"You can't prove a negative"

Existence of God

Other examples

In the media

See also