12.1 Direct Evidence
Perceptual evidence can give us direct acquaintance with the facts which make a claim true. Testimony or memory can also make us acquainted with the facts perceived at another time or by another person. All three forms of evidence can give mistaken or misleading information at times, however.
Table of Contents
- 12.1 Direct Evidence
12.1.1 What is Evidence?
Evidence is information which increases the likelihood that a claim is true.
Justifying the Premises
“A wise man proportions his belief to the evidence.”
—David Hume, An Enquiry Concerning Human Understanding
Evidence is what justifies someone in believing the premises of an argument are true, what makes it rational to believe the premises. Evidence has to do with the soundness of an argument, rather than its validity.
Evidence for a proposition is information which increases the likelihood that the proposition is true; evidence against a proposition decreases the likelihood that it is true. When there is enough evidence for a proposition, then someone can be justified in believing it to be true, though just how much is “enough” is hard to say and may depend on the situation or what is at stake.
Some evidence is weaker and only increases the likelihood slightly; other evidence is stronger. There can be evidence for a proposition, without the proposition being likely. For instance, the fact that a person’s fingerprints were at the crime scene increases rather than decreases the likelihood that she committed the crime, but it still might be very weak evidence, particularly if the crime scene was a shopping mall at which thousands of people’s fingerprints can be found.
There can be strong evidence for a proposition, and yet the proposition is false. For instance, it might be that multiple witnesses identify someone as the criminal, and that the tools used in the crime are found in her car, and that she had a motive for the crime, and that she had told people she planned to do the crime, and that she has no alibi, and as a result of overwhelming evidence, she is convicted by a jury. In spite of this, she might be innocent, and perhaps years later DNA evidence clears her name. Conversely, there may be only weak evidence for a proposition, and yet the proposition is true. For instance, a criminal may be very good at hiding his tracks, and no one would suspect him, and nothing would link him to the crime. It would be irrational for anybody (besides himself) to believe him to be the criminal. Nonetheless, he might in fact be the criminal.
Still, despite the fact that evidence is not truth, an intellectual virtuous person who desires the truth will set their beliefs in proportion to the evidence. The alternative, believing contrary to the evidence, can only be justified by some extrinsic reason — for instance, maintaining the belief that a relationship will not break up because the act of holding the belief makes it more likely the relationship will weather the storm; or believing that one will survive an illness with a high mortality rate because there is no other way to survive.
Types of Justification
The most basic type of evidence is the evidence which an experience gives of itself. For instance, my evidence that I am in pain is my pain itself, and my evidence that something smells bad is my own experience of smell. My evidence that I am thinking this thought right now is this thought which I am thinking. Most evidence is not like this, though. Instead, most evidence involves an experience which justifies a belief about something besides the experience itself.
We can divide justification into two categories. Inferential justification is a case where evidence about one thing, P, can be used to justify a belief about something else, Q, through a process of reasoning or inference. Direct justification is a case where my evidence of P justifies a belief that P. Direct evidence is traditionally thought to come from perception, testimony, and memory. For instance, seeing human footprints in the mud gives me direct justification in believing there are footprints in the mud, and inferential justification for believing that a person walked through the mud who left the footprints. Seeing a cat on the wall directly justifies me in believing that there is a cat on the wall, without any process of reasoning or inference, and inferentially justifies me in believing that the cat is getting food and water from somewhere.
12.1.2 Using Evidence to Defend a Premise
Black Swans falsify the claim that all swans are white.
Particular and Universal Claims
Suppose we want to use evidence to support the following argument:
P1. All roses are red.
P2. Some flowers at the store are roses.
C. Some flowers at the store are red.
Or this one:
P3. No carrots are purple.
P4. Some things in my lunch are purple.
C. Some things in my lunch are not carrots.
We recognize both of these as valid arguments, given the form of the argument. We want to inquire whether the argument is also sound, or whether the premises are actually true. To do that, we’d need to determine how to use evidence to evaluate each of the premises. That will depend on whether the premises are universal affirmative claims (P1 and P3), or whether they are particular claims (P2 and P4).
Evidence directly confirms particular claims. For instance, seeing roses in the store confirms P2, and seeing purple things in my lunch confirms P4. Every observation someone makes, or experience someone has, or every bit of data someone collects, serves as evidence of some particular claim about the existence of something. My experiences can directly confirm, for instance, that some cats meow, some dogs bark, some drivers run red lights, some CEOs are liars, some politicians want special privileges, some birds fly, some fish swim, and some swans are white. All direct evidence is evidence of a particular.
Evidence doesn’t directly confirm universal claims, generally speaking. Claims that All S are P are only true if there are no exceptions of an S which isn’t a P. There is no way to rule out that one hasn’t failed to observe the exception, however. Famously, Europeans used to believe that all swans were white, because they had only experienced white swans and assumed they had experienced all of the swans. When Europeans encountered black swans in Australia, they realized their beliefs were false. Similarly, evidence can’t confirm that all fish swim, all birds fly, all politicians want special privileges, all CEOs are liars, all drivers run red lights, all dogs bark, or all cats meow. Even if you have never seen an exception to the rule, there is no way to rule out the possibility of an exception that you haven’t seen.
Instead, we say that evidence directly disconfirms universal claims. We seek evidence in order to demonstrate that universal claims are false. For instance, observing black swans shows that “all swans are white” is false, observing ostriches shows that “all birds fly” is false, and flying fish show that “no fish fly” is false. Universal claims can be supported by evidence only insofar as we’ve gathered evidence and failed, at the present moment, to find any exceptions to them. For instance, the claim that “no birds fly” is very easy to disconfirm with evidence; “no mammals fly” can also be disconfirmed, but it takes a bit more work; “no cats fly”, on the other hand, is a claim which hasn’t been disconfirmed despite millennia of human observations of cats. So, the evidence supports “no cats fly”, at least tentatively, since no exception has yet been found.
Notably, evidence doesn’t directly disconfirm particular claims, generally speaking. Claims that Some S are P are true so long as there is some instance out there of an S which is a P. Even if we have never observed an S which is a P, not observing that there is something is not the same as observing that there is nothing. Again, there was no evidence for the claim “some swans are black” in Europe in the 16th century, though there was plenty of evidence to be found in a place Europeans weren’t looking: in Australia. Failing to observe evidence confirming some particular claim we would expect to observe if it were true, however, can give us inferential justification against that particular claim.
12.1.3 Perceptual Evidence
The most direct source of knowledge is perception.
Observations
We get perceptual evidence through our senses. For instance, seeing a kite flying in the air is evidence that a kite is flying in the air. Hearing the sound ‘meow’ is evidence of a cat. Feeling the moisture in the air is evidence that the air is humid. Observations give us evidence about how the world is at the moment we are observing it.
There are limitations to this evidence, though. First, we can misperceive something that we see, as when a straw in water looks bent when in fact it is straight, or we can hallucinate something that isn’t there at all, as when seeing a mirage of water on a hot desert highway. So, the fact that multiple people observe an event is stronger evidence that it happens than just one person observing it. Second, our perceptions come from a particular angle or perspective: when driving, I see the front of my car but not the back of it. Witnesses of a car accident, who have seen a fast-moving event from different angles, often describe it quite differently. So, a composite sketch of observations from multiple perspectives is going to create a clearer picture than one drawn from only one angle. Third, we don’t observe what happens when we aren’t watching: it is a common story for parents to be surprised at how different their children are when away from home. So, repeated observations in different circumstances are more reliable than one-time observations, or observations only in the same circumstances.
Measurement
Measurement is a tool to maintain consistency between repeated observations. Measurement does not make an observation more accurate or more precise. For instance, if you can clearly see exactly how tall somebody is, pulling out a tape measure does not help you see the person more clearly or accurately: the person will appear to be exactly the same height as they did without the tape measure. Measurements of observations are always less precise than unmeasured reality. For instance, if I step on an electronic scale which measures my weight in pounds, the scale will return a value to the nearest one-tenth of a pound. If it reports my weight as 202.8lbs, this means my real weight falls somewhere between 202.75 and 202.85 lbs.
Instead, what measurements do is provide us with a consistent standard which we can use to compare observations between different people or at different times, where that standard doesn’t rely on details that are difficult to remember. Have I gained or lost weight over the last week? Comparing my weights on the scale in pounds from last week to this week is far more reliable than comparing my memory of how heavy I felt last week. Who is taller, your tallest friend or my tallest friend? Even if we can never get our respective tallest friends in the same room together, if we measure each of them with a standardized measuring tape, we can compare our observations and determine who is the tallest.
Inferences Based on Observations
It is difficult, but very important, to distinguish what someone actually observes from an inference they make on the basis of an observation. For example, suppose that you observe that a person standing in line at the grocery store has a clenched jaw, is tapping her foot rapidly, frequently sighs and looks at her watch, and speaks curtly to the cashier. You might infer that the person wants to get out of the store quickly, but you haven’t actually observed the other person’s wants, you’ve only observed their behaviors. Again, suppose that you observe that the “Open” sign is lighted in a store and all of the lights are on. You would be right to infer from this that the store is open, but unless you walk up and open the door, you haven’t actually observed that the store is open.
While observations give us direct evidence of something, inferences give us only indirect evidence. The inferences we make on the basis of what we observe tend to rely on other premises. For instance, suppose that I observe a man standing on the edge of a bridge. I infer that the person is considering jumping off the bridge, and I call the police for help. My inference could be constructed into an argument:
1. A man is standing on the edge of a bridge.
2. If a man is standing on the edge of a bridge, then they are considering jumping off the bridge.
C. A man is considering jumping off the bridge (1, 2 MP).
This inference might be a good one which saves somebody’s life. But the inference might also be a mistaken one: I haven’t seen, for instance, that the man has a safety harness as well as an expensive camera, and in fact he is filming.
Again, while driving, I might see somebody’s right turn signal in front of me turn on, and I infer from this that the person is about to turn right. While this is a reasonable conclusion to draw, I don’t actually see the person turning right (which hasn’t happened yet), but only the turn signal. The process of inference looks like this:
1. The driver has their right turn signal on.
2. If the driver has their right turn signal on, then they will soon turn right.
C. The driver will soon turn right. (1, 2 MP)
Premise 2 might be false, however. After all, it is possible that the driver has turned the signal on by mistake, or left it on by mistake, or intends to turn right far up the road but has started preparing in advance. So, this is why it is useful to distinguish observations from inferences based on those observations.
12.1.4 Testimonial Evidence
Most of our knowledge comes through testimony from other people.
Testimony
You’ve probably heard the word “testimony” associated with the law, but philosophers use the word “Testimony” to mean not only testimony in court, but any everyday situation where someone asserts something and expects others to believe it on the basis of their assertion. Most of our knowledge comes through testimony. Every textbook you’ve ever read and every lecture you’ve ever heard is an example of testimony. When a friend tells you a story about something that happened, what you are hearing is testimony. When you ask a stranger for advice or directions, you accept what they say as testimony. When scientists report their results to one another in journals, they are relying on testimony. We would know very little if we were limited to only what we directly saw or heard ourselves, and so the testimony of others is an important source of evidence.
Reliable Sources
Not all testimony is equally credible, though. Some sources are more reliable than others. Because any sign that a source is credible could potentially be counterfeited, distinguishing credible from non-credible testimony can often be difficult, and there are no hard and fast rules about how to do so. There are, however, a few general “rules of thumb” which a logic student can use to evaluate the reliability of a source. Here are eight criteria which tend, generally speaking, to make a source more credible.
- Confirmation. Claims are more credible when confirmed by further evidence from another, independent source. The more independent the source’s perspective on the event, the stronger the corroboration provided. For instance, a pedestrian who witnesses a car accident may provide stronger corroborating evidence of a driver’s story than the passenger in the driver’s car. A lack of corroboration does not necessarily count against a claim if one would not expect more evidence to exist if the claim were true: for instance, claims about events with few witnesses, or events in the distant past. It does count against a claim where one would expect corroboration, however, such as a claim about a very recent and very public event.
- Easy Disconfirmation. Claims are more credible when there is no disconfirming evidence, and yet they could have been easily be disconfirmed by evidence if they were false, or where there would likely be disconfirming evidence if the claim were false. On the other hand, testimony is less trustworthy in cases where there is no risk of disconfirmation, and so little chance of being caught lying.
- Consistency. Claims are, obviously, more credible when they are consistent rather than contradictory. A source which contradicts itself must have, at some point, spoken falsely. Someone who is lying will often avoid saying too much, because they recognize there is a risk of accidentally contradicting themselves if they do so. Not all inconsistencies count equally, however: sometimes small inconsistencies are evidence of honesty, because they are evidence the person hasn’t carefully rehearsed or planned their story in advance.
- Relevant details. Testimony about an event ought to contain many relevant details about the event, which could then, in turn, be confirmed or disconfirmed, or found to be consistent or inconsistent with the rest of the person’s testimony. By contrast, having many irrelevant details is often a sign that someone is lying, as is having few details and a tendency to revert to talking in broad generalities whenever asked to discuss a specific claim.
- Neutrality. Testimony is more credible when the person giving the testimony has little to gain from being believed. In contrast, testimony is suspect (though not necessarily false) when it is someone’s self-interest to make the claim that they are making, or to have others believe it to be true: including cases where they are acting under political pressure, or under social pressure. The bandwagon effect can lead people to do or say things simply because others around them do so; when the person is removed from the social situation, they may then admit to not believing their own claim.
- Proximity. Testimony is more credible when the person giving it has direct acquaintance with the events their claims are about, or direct acquaintance with first-hand sources. This is opposed to cases where someone is distant from the information, such as testimony about someone else’s testimony about someone else’s testimony, or hearsay. Because of this, sources which track and verify their own sources of information are far more trustworthy than those which do not cite or bother to track their sources, since good scholarship indicates an interest in being right, rather than merely being believed to be right.
- Expertise. An expert source which is unlikely to have misinterpreted or misunderstood their observations is more reliable than a source which lacks expertise, and which might be honestly confused about what they observed. For instance, a laboratory report written by a student who has used the equipment before is more likely to be accurate than one written by a student using it for the first time. Establishing expertise requires being open to objections or questions from one’s informed peers, including those who disagree, and being recognized as an expert by those peers. This is why many journals utilize peer review: requiring that peers critique and try to poke holes in one anothers’ claims, and allowing discussion and debate, reduces the risk of circular reasoning.
- Reputation. A reputable source is one which has a past record of making true claims, and which receives social status in return for its reliability in the past, so that if now their claims were shown false, they would risk losing their reputation. By contrast, a person who is known to have a history of making false claims and getting away with making them, or a source which has little to lose if shown wrong (like a website that specializes in attention-grabbing headlines) is less trustworthy.
Of course, testimony that seems to come from a less credible source can later turn out to be true, and testimony that seems very credible can later turn out to be false. These are not enduring, exceptionless, principles, just general rules of thumb.
A Word on Testimonial Injustice
We often evaluate “credibility” on the basis of a gut feeling that someone knows what they are talking about, rather than by thinking through why we consider the source credible. One reason it is important to evaluate testimony based on objective criteria, rather than merely gut feelings, is that we are often influenced by unconscious biases to give too much credibility to the testimony of people who look or sound like the “image” of authority in our society, and too little credibility to the testimony of those who do not match that image. “Testimonial injustice”, occurs, according to epistemologist Miranda Fricker, when “a speaker receives an unfair deficit of credibility from a hearer owing to prejudice on the hearer’s part.” These prejudices can include factors like gender, race, disability, class, or status. To avoid this, it is important to be able to think through reasons why some testimony seems more or less trustworthy to us, rather than simply relying on an impression that someone seems more, or less, reliable.
12.1.5 Evidence From Memory
Memory allows us to retain knowledge as the years go by.
Memory as a Source of Evidence
Memory is an important source of evidence; without relying on information from memories of the past, we couldn’t even begin to interpret our evidence from perception or testimony in the present. Your ability to recognize what you are reading right now as words, and to know what those words mean, relies on memory. Memory is, in general, reliable; if memory wasn’t generally reliable, we wouldn’t have any reason to be surprised or to complain in those cases where it fails.
At the same time, memory is not a “time machine” which allows us to, literally, perceive the past. Our memories are reconstructed each time we recall them, and in the process of trying to make sense of what we remember, we often add to or change what we remember. Whenever recollecting things we tend to recount information in a narrative structure, a coherent “story” with a beginning, middle, and end, much like we might read in a book or watch in a television episode. The information we receive, however, does not come prepackaged in a narrative structure. Information that doesn’t fit into a narrative becomes easier to reject than information which fits nicely within a story.
Failure by Forgetfulness
Harvard psychologist Daniel Schacter has identified “seven deadly sins of memory”, seven ways in which memory may fail us, six of which are relevant to our study of evidence. The first three involve forgetfulness:
| Sin | Description | Example |
| Transience | Accessibility of memory decreases over time | Forget events that occurred long ago |
| Absentmindedness | Forgetting caused by lapses in attention | Forget where your phone is |
| Blocking | Accessibility of information is temporarily blocked | Tip of the tongue |
Let’s look at the first sin of the forgetting errors: transience, which means that memories can fade over time. Here’s an example of how this happens. Nathan’s English teacher has assigned his students to read the novel To Kill a Mockingbird. Nathan comes home from school and tells his mom he has to read this book for class. “Oh, I loved that book!” she says. Nathan asks her what the book is about, and after some hesitation she says, “Well . . . I know I read the book in high school, and I remember that one of the main characters is named Scout, and her father is an attorney, but I honestly don’t remember anything else.” Nathan wonders if his mother actually read the book, and his mother is surprised she can’t recall the plot. What is going on here is storage decay: unused information tends to fade with the passage of time.
Cynthia, a psychologist, recalls a time when she recently committed the memory error of absent mindedness.
“When I was completing court-ordered psychological evaluations, each time I went to the court, I was issued a temporary identification card with a magnetic strip which would open otherwise locked doors. As you can imagine, in a courtroom, this identification is valuable and important and no one wanted it to be lost or be picked up by a criminal. At the end of the day, I would hand in my temporary identification. One day, when I was almost done with an evaluation, my daughter’s daycare called and said she was sick and needed to be picked up. It was flu season, I didn’t know how sick she was, and I was concerned. I finished up the evaluation in the next ten minutes, packed up my tools, and rushed to drive to my daughter’s day care. After I picked up my daughter, I could not remember if I had handed back my identification or if I had left it sitting out on a table. I immediately called the court to check. It turned out that I had handed back my identification. Why could I not remember that?”
The third memory error is blocking, the frustrating experience most of us have had of having information “at the tip of our tongue” but unable to reproduce it. Imagine someone says to you: “I just went and saw this movie called Oblivion, and it had that famous actor in it. Oh, what’s his name? He’s been in all of those movies, like The Shawshank Redemption and The Dark Knight trilogy. I think he’s even won an Oscar. Oh gosh, I can picture his face in my mind, and hear his distinctive voice, but I just can’t think of his name! This is going to bug me until I can remember it!” Their memory will return the moment you say, “You mean Morgan Freeman?” We have a silly colloquial term for this (a “brain fart”), but the phenomenon has been long recognized. The philosopher William James wrote:
“A sort of wraith of the name is in it, beckoning us in a given direction, making us at moments tingle with the sense of our closeness and then letting us sink back without the longed-for term.” (Principles of Psychology, Ch. 9, 1890)
Failure by Distortion
The next three sins of memory involve cases where we are able to recollect an event, but the process of reconstructing our memories leads to distortion.
| Sin | Description | Example |
| Misattribution | Source of memory is confused | Recalling a dream memory as a waking memory |
| Suggestibility | False memories | Result from leading questions |
| Bias | Memories distorted by current belief system | Align memories to current beliefs |
Misattribution happens when you confuse the source of your information. Let’s say Alejandro was dating Lucia and they saw the first Hobbit movie together. Then they broke up and Alejandro saw the second Hobbit movie with someone else. Later that year, Alejandro and Lucia get back together. One day, they are discussing how the Hobbit books and movies are different and Alejandro says to Lucia, “I loved watching the second movie with you and seeing you jump out of your seat during that super scary part.” When Lucia responded with a puzzled and then angry look, Alejandro realized he’d committed the error of misattribution.
The second distortion error is suggestibility. Suggestibility is similar to misattribution, since it also involves false memories, but it’s different. With misattribution you create the false memory entirely on your own, when your mind seeks to match your memory to information from external sources. With suggestibility, it comes from someone else, such as a therapist or police interviewer asking leading questions of a witness during an interview. For instance, a witness might not remember the color of a robber’s get-away vehicle, but through a process of leading questions they begin to report remembering a color the interviewer suggested to them.
Memories can also be affected by bias, which is the final distortion error. Schacter (2001) says that your feelings and view of the world can actually distort your memory of past events. There are several types of bias, for example:
- Stereotypical bias involves racial and gender biases.
- Egocentric bias involves enhancing our memories to think more highly of ourselves.
- Hindsight bias happens when we think an outcome was inevitable after the fact. This is the “I knew it all along” phenomenon. We remember untrue events that seem to confirm that we knew the outcome all along.
We unconsciously try to match our memories to fit our underlying beliefs about the world, or to make them fit into a coherent story that we could more easily recount to others. For example, we may “adjust” our memories of our own past actions or motivations, or the past actions or motivations of others around us, in order to fit the story we currently tell about our lives: the story of overcoming the odds stacked against us, the story of being in the right yet always wronged by others, the story of simply having to do things the way we did without much choice in the matter, the story of having freely chosen things which we didn’t really choose, or so on, erasing much of the nuance and complexity of what really happened.
Introspection, Imagination, and Rational Insight
Three other sources of evidence which do not count as memory, but which have some similarities to memory, are introspection, imagination,and rational insight. They are like memory insofar as they involve looking ‘inward’ into our own minds, private experiences which others can’t share. They differ in what they provide information about. Since they are less common sources of evidence, we’ll discuss them here only briefly.
- Introspection provides me with evidence about what I myself am currently thinking or feeling. For instance, I know that I currently feel tired, that there is a pain in my left leg, and that I am thinking about maple syrup. We each have a perspective on the workings of our own minds that others do not have.
- Imagination provides us with evidence about what could have been, what might have been, and what would have been. Our ability to coherently imagine something, like a flying reindeer, does not give us evidence that it actually exists, of course. It does, however, give us a reason to think that it could have existed. Imagine for a moment what you would do if the smoke detector went off, or what would happen if an ice-cube were placed in a cup of hot water. What you just imagined provides some evidence about what would happen, although of course the way we imagine things is not always the way things are. Now, imagine things going differently than you just imagined how they would go: your imagination gives you information about how things might have gone differently.
- Rational insight provides us with the basic information we use to make sense of everything else: the principles of logic, the basics of arithmetic and geometry, and our sense of how things must be or have to be. We might say that rational insight is the converse of imagination: our inability to imagine something being any different gives us a reason to think that it must be the way that it is. For example, it seems hard to imagine the world working in a way where similar inputs didn’t tend to produce similar outputs, or similar causes didn’t produce similar effects. We’ll turn in the next submodule to considering this kind of evidence from induction.
Submodule 12.1 Quiz
Licenses and Attributions
Key Sources:
- Watson, Jeffrey (2019). Introduction to Logic. Licensed under: (CC BY-SA).
- CC LICENSED CONTENT. Modified from Psychology. Authored by: OpenStax College. Located at: Open Stax CNX – Psychology. License: CC BY: Attribution. License Terms: Download for free at Open Stax CNX – Psychology.
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