Two Ways of Being the Same

Lena and her brother Tom were each given a mug for their birthday. The two mugs are exactly alike: blue, with a little orange fox on the side. One morning Lena sees Tom drinking from a fox mug and says, "That's my mug!" Tom says, "No, it's the same as yours - but it's mine." Who is right? It depends on what "the same" means.

Alike, or one and the same?

"The same" has two different meanings in everyday talk.

The first meaning is exactly alike: two things with the same properties. Lena's mug and Tom's mug are exactly alike. Same colour, same shape, same fox. But there are two of them. If Tom breaks his, Lena's is still on the shelf.

The second meaning is the same one: not two things, but one. When Lena asks "Is that my mug?", she isn't asking whether it looks like hers. She is asking whether it is hers - the very mug she was given, and not another one just like it.

Here is how to tell the two apart. Ask: "How many are there?" Two things that are exactly alike are still two. Something that is the same one is one.

One thing with two names

Long ago, people in many lands saw a very bright star low in the sky just before sunrise. They called it the Morning Star. They also saw a very bright star low in the sky just after sunset, and called it the Evening Star. They thought these were two different stars.

Later, astronomers worked out that they were one and the same: the planet Venus, seen at different times. Nothing about Venus changed. What people found out was that two names pointed to one thing.

The same one, but not alike

The two meanings can come apart the other way too. In the Things and Their Properties lesson, Kofi's apple went from red and crunchy to brown and soft. The apple on Monday and the apple a week later are not exactly alike. But they are the same one: there was only ever one apple.

So a thing can change its properties and still be the same one. That raises the question of the next lesson: how much can a thing change and still be the same one?

Try it at home

1. Listen for the word "same" today, and write down three times you hear it.
2. For each, ask: "How many are there?" Does it mean exactly alike, or the same one?
3. Find one thing at home that has changed a lot but is still the same one.

Words to know

• exactly alike - having all the same properties, even if there are two of them
• the same one - one thing, not two; the very thing, and not another like it

Big idea

"the same" can mean exactly alike or the same one. Two things can be exactly alike and still be two; one thing can change and still be the same one. Most puzzles about sameness come from mixing up the two.