Validity facts for kids

Validity means something is correct, proper, or makes sense. We use this word in everyday talks and also in logic, which is about how we think and reason.

When we say something is valid in daily life, it means it's in the right form or can be used. For example, a ticket to a concert is valid if it lets you get in. If it's expired, it's not valid.

What Does "Valid" Mean in Real Life?

Many things in our lives need to be valid to work correctly:

• An argument is valid if it makes good sense and can be supported with facts. It means the reasons given are strong and convincing.
• A contract is valid if it's legally binding. This means it follows the rules of law and can be enforced. Both sides must follow what the contract says.
• A banknote (like a dollar bill) is valid if you can use it to buy things. If it's fake or too old to be used, it's not valid.
• A passport is valid if it lets you travel in and out of countries. If your passport has expired, it is no longer valid for travel.
• A will is valid if it was made correctly and approved by a court. This makes sure a person's wishes for their belongings are followed after they pass away.

In all these cases, "valid" means something is sound, correct, and works as it should in a specific situation.

Validity in Logic

In logic, validity has a very specific meaning. It's not about whether something is "true" in the real world. Instead, it's about how an argument is built.

Validity in logic looks at the structure of an argument. It checks if the conclusion must be true if the premises (the starting statements) are true. It doesn't matter if the premises are actually true or not.

Let's look at an example of a valid argument, called a syllogism:

• All men are mortal. (This is a premise)
• Socrates is a man. (This is another premise)
• Therefore, Socrates is mortal. (This is the conclusion)

In this example, if the first two statements are true, then the conclusion has to be true. The argument is valid because of its structure.

Here's another example that is also valid, even though it talks about something that isn't true in real life:

• All cups are green.
• Socrates is a cup.
• Therefore, Socrates is green.

This argument is valid because if the first two statements were true, the conclusion would logically follow. The structure is correct. But we know Socrates was not a cup, and he wasn't green! So, while the argument is valid, its statements are not true.

Valid vs. Sound Arguments

It's important to know the difference between a valid argument and a sound argument.

• A deductive argument is valid if its conclusion logically follows from its premises. The structure is correct.
• A deductive argument is sound if it is valid AND all of its premises are actually true.

Here's an example of an argument that is valid but not sound:

• All animals live on Mars. (This premise is not true)
• All humans are animals. (This premise is true)
• Therefore, all humans live on Mars. (This conclusion is not true)

This argument is valid because if all animals lived on Mars, and humans are animals, then humans would logically have to live on Mars. The structure is good. However, the argument is not sound because its first premise ("All animals live on Mars") is false. For an argument to be sound, both its structure must be valid and all its starting statements must be true.