Another source of evidence is observation.

For example, this ad argues that the Vision saucepan (made from colexion!) is more durable than an aluminium saucepan. To support that claim, the ad lets us observe the following demonstration:

Advertisers love dramatic product demonstrations.

Video is compelling, but we can capture observations in all sorts of formats.

For Chelsea Black, a marine biologist, these photos of a shark's dorsal fin provided observational evidence of a remarkable healing ability:

Changes in the dorsal fin from 2022 and 2023 Josh Schellenberg and John Moore

Flash forward to one year later, the summer of 2023. I received several photos of silky sharks from John Moore. In the many shark photos he sent, I noticed a silky shark with an oddly shaped dorsal fin.

I knew immediately it had to be #409834 from the previous summer. A few days later, John was able to get close enough to photograph the ID tag to confirm my hunch. Josh Schellenberg also spotted and photographed #409834. With both John’s and Josh’s photos, I was able to compare the healed dorsal fin with the freshly injured one.

I wasn’t expecting to make a groundbreaking discovery. Simple curiosity led me to start analyzing the photos. But the revelation was astonishing: Not only had the wound completely healed, but the 2023 dorsal fin was 10.7% larger in size than it was after the injury in 2022. New fin tissue had regenerated.

Like any material, photos and videos can be faked.

For example, this photo was used in 1920 as evidence for the existence of fairies:

Black and white photo of a woman looking at a fairy in surprise.

In 1978 the magician and scientific sceptic James Randi and a team from the Committee for the Scientific Investigation of Claims of the Paranormal examined the photographs, using a "computer enhancement process". They concluded that the photographs were fakes, and that strings could be seen supporting the fairies.

Geoffrey Crawley, editor of the British Journal of Photography, undertook a "major scientific investigation of the photographs and the events surrounding them", published between 1982 and 1983, "the first major postwar analysis of the affair". He also concluded that the pictures were fakes.

The photo is observational evidence, but it's fake.

FYI The evidence in the snippet is what we call expert testimony (it's not observational evidence). We'll talk about expert opinion later in this lesson.

We use observational evidence in art & media criticism whenever we quote from books, clip from audio, or screengrab from movies, games, and other media.

For example, the YouTuber in this snippet uses footage from Death Stranding to make a case that Order #14: Port Knot City qualifies as a "legendary" mission in gaming history:

There's one specific mission early on in the game that accentuates everything the title is trying to accomplish so perfectly, showing why not every mission has to be about daring set pieces and massive explosions. That mission is Order Number 14: Port Knot City. 

You set out on this massive venture, carefully walking across rivers and taking in the extravagant nature all around you. It's only when you finally get to the hill that you encounter your first major enemies. But the real best part of this mission, and why it's so memorable, is still yet to come.

After finally making your way past these enemies to the top of the hill, you're met with a massive sprawling view at the top of a mountain, with steep cliff edges at every side leading all the way to Port Knot City adjacent to the coast.

Just as you're starting to take in this amazing view, the best in the game up to this point, a song starts to blare through your speakers, one of pure beauty and resonance. It seems to almost fill the void of the canyons below with its melody. For the first time in the game, you really start to understand what makes it so special: simply looking out into the distance and seeing such a barren and dead world come to life, along with that sense of cold from the environment and warmth from the song that unite into pure bliss.

The video is observational evidence: you can see with your own eyes what FranklyGaming is talking about.

Notice that still leaves you room to disagree with his argument! You might look at the same evidence and conclude that the mission is not good at all.

You might also wonder if the transcript is an observation or a story of personal experience. It's kind of both.

Retelling your observation of an event in which you were a participant is necessarily a story of your own experience.

For example, we called Pliny's letter about the eruption of Mt Vesuvius a personal story, but it could also be called observational evidence.

The takeaway here is that some pieces of evidence can fit multiple categories, and that's fine.

The point of these categories is not to play matching games; it's to help you identify the inherent strengths & weaknesses of a piece of evidence.

For example, a problem with personal stories as evidence is we often have to take the speaker's word for it. Pliny's evidence is more like a personal story because we can no longer see what he observed; whereas we can immediately see for ourselves what FranklyGaming observed.

But that's not to say all observations can be repeated!

There's a lot of observational evidence where, if we are going to believe it, we just have to take the observer's word about what they observed. 

(Also, observations about games are ambiguous because we experience them. Descriptions of events in books or movies don't blur into personal experience as much because the line between the observer and the action is more defined.)

Another type of observational evidence is when we use direct quotes as evidence of what people have written or said.

The writer of this next snippet quotes a poem from James Russell Lowell as evidence of Lowell's passionate objection to slavery:

That slavery is central to Lowell’s moral and historical argument is foregrounded in the next stanza, where Lowell personifies slavery as the great moral adversary of his time:

Slavery, the earth-born Cyclops, fellest of the giant brood,
Sons of brutish Force and Darkness, who have drenched the earth with blood,
Famished in his self-made desert, blinded by our purer day,
Gropes in yet unblasted regions for his miserable prey;—
Shall we guide his gory fingers where our helpless children play? (67–68)

By describing slavery as a Cyclops, Lowell allows the classical learning of his readers to do some important work for him, in the same way that he used the biblical knowledge of his readers in earlier stanzas.

  • The snippet opens with a claim that Lowell strongly objected to slavery.
  • It quotes directly from Lowell's work, "observing" the relevant lines.
  • It concludes by articulating the reasoning that connects the evidence to the claim.

And we don't only quote in discrete chunks; quoted evidence can be taken in fragments and mixed in with commentary.

In this next snippet, the writer quotes several lines as evidence that "the journey of life" is a recurring theme in the Bible:

One of Jesus’s most famous parables tells the story of a traveler on the road from Jerusalem to Jericho (Luke 10:30–36). Along the way, he “fell among thieves, which stripped him of his raiment, and wounded him, and departed, leaving him half dead.” The perils of the road are accepted as a part of life, as is the subsequent behavior of other travelers, a priest and a Levite, who cross to the other side of the road rather than touching this poor man. It is the Samaritan who “went to him, and bound up his wounds, pouring in oil and wine, and set him on his own beast, and brought him to an inn, and took care of him.” This good Samaritan is apparently fully equipped, on a long journey, with a beast of burden, and knowledge of the inns along the way.

Jesus uses this famous story to set up his final question to the lawyers who are challenging his interpretation of the law and the definition of neighbors. He interweaves the message of morality with life experience, and fills it with movement and experiences from actual lives his audience will understand and remember. They all know this particular road to Jericho and the perils along the way.

This whole snippet is observational evidence, but some of it is summarised text and some of it is direct quotes.

Direct quotes are powerful because they show us what is actually there and they are often more vivid than summary descriptions.

Since quoting at length can slow down or obscure the argument being made, speakers will often summarise the bulk of the evidence and highlight only a few interesting or representative extracts.

Of course, we have to take it on trust that the speaker didn't cherry-pick their quotes!

Science, in particular, is powered by the systematic collection of observational evidence.

For example, Charles Darwin derived his theory of natural selection (which led to the theory of evolution) in part from systematic observations he made about variations between bird species on the Galapagos Islands:


The remaining land-birds form a most singular group of finches, related to each other in the structure of their beaks, short tails, form of body and plumage: there are thirteen species which Mr. Gould has divided into four sub-groups.

The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and even to that of a warbler.

The largest beak in the genus Geospiza is shown above in Fig. 1, and the smallest in Fig. 3; but instead of there being only one intermediate species, with a beak of the size shown in Fig. 2, there are no less than six species with insensibly graduated beaks. The beak of the sub-group Certhidea, is shown in Fig. 4. 

Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.

This snippet gives you a sense of how distinctive scientific observations are from other types of observation.

Darwin is being systematic:

  • He's observed many of these birds.
  • He's collected specimens, descriptions, & engravings.
  • He's organised his observations (in this instance, into what we'd call a classifying report).

And because this is early field observation, where he is recording observations for the sake of interest more than in the service of a particular argument, he does not make any strong claims.

Instead, he raises what he has begun to notice as an issue, which is that all these species seem to be variations on a theme. (And this question leads him, many years later, to propose a theory of natural selection.)

To make sure their observations are representative, scientific researchers must think carefully about what they observe and how they capture their evidence.

For example, these researchers wanted to see if people in wealthy vs poor cities around the world walked at different speeds:

Male and female walking speed over a distance of 60 feet was measured in at least two locations in main downtown areas in each city. Measurements were taken during main business hours on clear summer days. All locations were flat, unobstructed, had broad sidewalks, and were sufficiently uncrowded to allow pedestrians to move at potentially maximum speeds.

To control for the effects of socializing, only pedestrians walking alone were used. Children, individuals with obvious physical handicaps, and window-shoppers were not timed. Thirty-five men and 35 women were timed in most cities.

There is no evidence in this snippet. Instead, it's a description of the researchers' method for collecting their evidence.

As with Darwin's observations about species on the Galapagos Islands, these researchers have to be systematic.

They have an idea that people in rich and poor cities around the world will walk at different speeds.

But how do you measure that?

  • Do you measure how far someone walks in a set time, or how long it takes them to walk over a fixed distance?
  • How many people will you measure?
  • What ages? (Kids and old people walk slower than regular adults.)
  • What about men vs women? (Do they tend to walk at different speeds?)
  • Where will you conduct these observations? (People might walk faster or slower in particular areas of a city.)

These are all questions you need to answer if you want to publish your observations in a scientific study, which we'll talk about later in this lesson.

Let's play with some made-up observational evidence.

Here's a famous ad about how Burger King doesn't use any preservatives. The ad itself is observational evidence, but you can back it up with even more observational evidence (however ludicrous).

(You can describe a demonstration, use quotes, pretend to have scientific observational data, whatever you like.)

Support the claim that Whoppers are preservative free using made-up observational evidence. (~3-5 sentences)

Here's an example of an argument inspired by the Moldy Whopper, using observational evidence:

Day 36

None of the Whoppers are moldy.

The air is humid and all the windows are open. I even let Tobie lick them a few times, hoping his saliva would encourage growth.

No mold can be found on any of the ingredients in Whoppers #1-14. (Tobie ate #15; the licking got out of control.)

I am starting to believe they contain preservatives.

In a nutshell

  • Observational evidence is about witnessing phenomena, while not necessarily being a part of it.
  • That can mean photos, video, illustrations, and audio of observations.
  • It can also mean written descriptions, accounts, and records of observations.
  • It can mean samples of phenomena—e.g. collections of materials, or quotes and other fragments of material.
  • Like personal experiences, observational evidence can be personal and ad-hoc.
  • But most science is based on systematic, large-scale, repeated observations and measurements.


  • Demonstrations & examples let you see something with your own eyes—and seeing is believing! (Same goes for our other senses.)
  • Observation can be standardised and repeated in a way that personal experience can't, which means it can be at a larger scale and a longer time frame.


  • Not everything is easy to observe, or observe repeatedly under consistent conditions.
  • The way we observe something could be bad, leading us to capture the wrong data, insufficient data, or data with hidden errors.