Mill's Methods facts for kids

Mill's Methods are five special ways of thinking about how things cause other things to happen. A famous philosopher named John Stuart Mill wrote about these methods in his book A System of Logic in 1843. They help us figure out what causes a certain event or outcome.

Understanding Causes and Effects

When we try to understand why something happens, we are looking for its cause. Mill's Methods give us tools to investigate these connections. They help us find patterns and rule out things that are probably not the cause.

The Method of Agreement

If two or more instances of the phenomenon under investigation have only one circumstance in common, the circumstance in which alone all the instances agree, is the cause (or effect) of the given phenomenon.

—John Stuart Mill

Imagine you have many different situations where the same thing happens. The Method of Agreement says that if all these situations have only one thing in common, that common thing is likely the cause.

For example, let's say you and your friends all get a stomach ache after a school picnic.

• Friend 1 ate a hot dog, chips, and a cookie.
• Friend 2 ate a sandwich, chips, and a cookie.
• Friend 3 ate a hot dog, a salad, and a cookie.

The only food everyone ate was the cookie. So, using this method, you might guess the cookie caused the stomach aches.

This method helps us find something that is always present when an effect happens. If something is missing when the effect is there, it can't be the cause.

The Method of Difference

If an instance in which the phenomenon under investigation occurs, and an instance in which it does not occur, have every circumstance save one in common, that one occurring only in the former; the circumstance in which alone the two instances differ, is the effect, or cause, or an indispensable part of the cause, of the phenomenon.

—John Stuart Mill

This method is about comparing two situations that are almost exactly alike, except for one thing. If one situation has an outcome and the other doesn't, the one difference between them is probably the cause.

Think of it like this:

• You study for a test, get enough sleep, and eat breakfast. You get a good grade.
• Your friend studies for the test, gets enough sleep, but skips breakfast. Your friend gets a bad grade.

The only difference between your situation and your friend's is eating breakfast. So, the Method of Difference would suggest that eating breakfast might have helped you get a good grade.

This method is often used in controlled experiments. Scientists try to keep everything the same between two groups, except for the one thing they are testing.

The Joint Method of Agreement and Difference

If two or more instances in which the phenomenon occurs have only one circumstance in common, while two or more instances in which it does not occur have nothing in common save the absence of that circumstance; the circumstance in which alone the two sets of instances differ, is the effect, or cause, or a necessary part of the cause, of the phenomenon.

—John Stuart Mill

This method combines the first two. It looks for a common factor when an event happens, and also looks for the absence of that factor when the event does not happen.

Let's say you want to find out what causes plants to grow tall.

• You notice that all the tall plants in your garden got plenty of sunlight and water. (Method of Agreement)
• You also notice that all the short plants did not get enough sunlight, even if they got water. (Looking for the absence of the cause)

If sunlight is the only common thing among tall plants, and its absence is the only common thing among short plants, then sunlight is likely the cause of tall growth.

The Method of Residues

Subduct from any phenomenon such part as is known by previous inductions to be the effect of certain antecedents, and the residue of the phenomenon is the effect of the remaining antecedents.

—John Stuart Mill

This method is like solving a puzzle. If you know that certain parts of an effect are caused by certain things, and there's a leftover part of the effect, then that leftover part must be caused by whatever is left over from the causes.

Imagine you have a bag of mixed candies. You know that:

• The red candies weigh 100 grams.
• The blue candies weigh 50 grams.
• The total weight of the bag is 180 grams.

If you subtract the weight of the red and blue candies (100 + 50 = 150 grams) from the total weight (180 grams), you are left with 30 grams. This "residue" must be the weight of any other candies in the bag, like green ones.

This method helps us find new causes for unexplained parts of an event.

The Method of Concomitant Variations

Whatever phenomenon varies in any manner whenever another phenomenon varies in some particular manner, is either a cause or an effect of that phenomenon, or is connected with it through some fact of causation.

—John Stuart Mill

This method looks for things that change together. If one thing increases or decreases, and another thing also increases or decreases in a similar way, they might be connected.

For example, imagine you are watering a plant.

• If you give it a little water, it grows a little.
• If you give it more water, it grows more.
• If you give it too much water, it might stop growing or even shrink.

The amount of water and the plant's growth change together. This suggests that the amount of water is connected to how much the plant grows.

This method is different from the others because it doesn't just look for something being present or absent. It looks at how the amount or strength of something changes along with the outcome.

Why These Methods Matter

Mill's Methods are important because they give us a logical way to think about cause and effect. They are used in many fields, from science to social studies, to help us understand the world around us. They help us make better decisions by figuring out what truly causes things to happen.

See also

• Causal inference
• Controlled scientific experiments