Why Do You Think So?

Sara looks out of the window and says, "It will rain today." Her brother asks, "Why do you think so?" Sara has to give an answer. What kind of answer would make her brother believe her?

An idea and a reason

Sara answers, "Because the sky is full of dark clouds."

Now there are two parts. The first part is the idea: "It will rain today." The second part is the reason: "the sky is full of dark clouds". A reason is something we say to show why an idea is worth believing.

Reasoning means using reasons to get to an idea, or to check one. You reason all the time, often without noticing it:

• "The shop must be closed - all the lights are off."
• "Ali isn't at school, so he is probably ill."
• "I should take a coat, because it is cold outside."

In each sentence, one part is the idea and the other part is the reason for it.

Not every reason helps

Imagine Sara had answered differently: "It will rain today, because I want to stay at home."

Wanting to stay at home is a real reason for something - but not for rain. The sky doesn't care what Sara wants. Dark clouds, on the other hand, really do have something to do with rain: rain falls from clouds.

So the question is never just "Did they give a reason?" It is "Does this reason really support the idea?" To support an idea means to make it more likely to be true. This whole course is about that question.

Logic

The study of good and bad reasoning is called logic. It is one of the oldest subjects people have studied: thinkers in ancient Greece, India and China all wrote about it more than 2,000 years ago. Logic doesn't tell you what to believe. It helps you check whether your reasons, and other people's reasons, really lead where they say they do.

Try it at home

1. Take a notebook and write "Why do you think so?" at the top of a page.
2. For one day, listen for sentences with "because" or "so" in them - at home, at school, in adverts, in videos.
3. Write down three of them. Underline the idea once and the reason twice.
4. For each one, ask: does this reason really support the idea?

Words to know

• reason - something said to show why an idea is worth believing
• reasoning - using reasons to get to an idea, or to check one
• support - a reason supports an idea when it makes the idea more likely to be true
• logic - the study of good and bad reasoning

Big idea

When someone tells you an idea, you can always ask "Why do you think so?" A good answer gives a reason that really supports the idea, not just any reason at all.