What is evidence?

Good arguments are built from lots of pieces of evidence

Strong arguments use reasoning—cause & effect or criteria & match—to organise and connect those pieces of evidence to reach a conclusion.

In an ideal world, if the evidence & reasoning are good, then people should agree with the argument.

For example, do you agree with the claim that the moon has become a key target for exploration missions?

In recent years, the Moon has become a key target for exploration missions. For instance, just last year we witnessed Russia’s attempted landing of its Luna 25 probe and the first successful ISRO Moon shot, Chandrayaan-3. 

Meanwhile, the US aims to return humans to the Moon through their Artemis programme while also supporting commercial companies in their quest to reestablish a viable presence there.

NASA and its international partners aim to eventually place a crewed space station in lunar orbit, the Gateway Lunar Space Station. 

Simultaneously, China continues its successful, carefully planned Chang'e project. The Asian powerhouse is working towards establishing its own International Lunar Research Station. That Chinese–Russian project is promoted as “open to all interested countries and international partners”.

This snippet consists of:

  • One main claim (the moon is a key target for exploration missions).
  • Four pieces of evidence (a list of current moon missions from countries around the world: Russia, India, the US, and China).

Notice how this is a valuational claim? That means you'd expect the evidence to be things that show other countries are keen on exploring the moon, which is what the writer provides.

And do you agree that the best plan to save an Icelandic town from a lava flow is to build a barrier or diversion?

Humans have tried many ways to stop lava in the past, from attempting to freeze it in place by cooling it with sea water, to using explosives to disrupt its supply, to building earthen barriers. 

It’s too soon to say if Iceland’s earthworks will succeed in saving Grindavík, a town of about 3,500 residents, and a nearby geothermal power plant. As a volcanologist, I follow these methods. The most successful attempts to stop or reroute lava have involved diversions like Iceland’s. 


In 1973, Icelanders attempted the most famous “lava freezing” experiment. They used water hoses from a flotilla of small boats and fishing vessels to protect the small island community of Heimaey from the Eldfell volcano’s lava.

The lava flows were threatening to close off the harbor, which is critical to the region’s fishing industry and a lifeline to the Icelandic mainland. The eruption ended before the success of the strategy could be properly evaluated, but the harbor survived.


Hawaiians used explosives dropped from planes in 1935 and 1942 to try to disrupt lava flows from Mauna Loa volcano that were threatening the town of Hilo on the Big Island. 

The idea was to disrupt the channels or lava tubes in the volcano that were supplying lava to the surface. Neither attempt was successful. The explosions created new channels, but the newly formed lava flows soon rejoined the original lava channel.


Most recent efforts have focused instead on a third strategy: building dams or ditches in an attempt to divert the lava’s flow toward a different path of steepest descent, into a different “lavashed,” a concept similar to a watershed but where lava would naturally flow.

Results have been mixed, but diversion can be successful if the lava flow can be clearly diverted into a distinct area where lava would naturally flow – without threatening a different community in the process.

The main claim is that the most effective way to stop lava is to divert it. The evidence consists of three examples of lava-stopping methods, only one of which could be said to have worked.

(The writer also limits their claim and adds their credentials as supporting evidence.)

We can see that in both snippets, the evidence makes up the bulk of the argument.

But what actually IS evidence? And what is GOOD evidence?

These are two really important questions.

  • The first question is quite easy to answer.
  • The second question is very challenging.

This lesson is about the easy question! 😂

Evidence is whatever material can be used to support a claim

That means evidence can be almost anything—stories, photos, objects, statistics, opinions—depending on how it's used.

In this lesson, we'll look at some of the most common types of material that people use as evidence, and talk about their strengths & weaknesses.

This will help you identify evidence in arguments that you read, and think about what evidence you might include in arguments that you make.

This is a big question!

  • Not all evidence is good evidence: some of it is faulty, incomplete, inaccurate, or completely made up.
  • And not all evidence is used properly in arguments. Even good evidence can become bad evidence if it's used incorrectly.
  • Sometimes bad evidence is obvious, but often it can be difficult to tell.
  • Evaluating a single piece of evidence might require a lot of time, effort, and expertise.
  • If we don't have the necessary time and expertise, or don't want to make the effort, we have to decide if we want to trust the source of the evidence.
  • And deciding who to trust can also be challenging, and require time, effort & expertise!

This is such a big problem that philosophers, scientists, researchers, and lawyers have been debating it for hundreds, if not thousands, of years.

It's not all bad news! There are some answers! But you can see why it might be too complex to fit into this lesson.

We will touch on it, but we'll leave a more detailed discussion for another lesson.

If you're interested in arguments and you want to take them seriously, keep the question of what makes good vs bad evidence in the back of your mind. See if you can come up with any criteria!

Now let's look at some different types of evidence!