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# Anniversaries, milestones, categories, and round numbers

## We impose a structure on numbers. Why does that matter?

Hwy 171 sign

This is the 171st entry I have written for Ulterior Motives. That seems like a strange announcement to make. When reading entries by my fellow bloggers, I have seen people introduce themselves by saying this is their first entry. I have seen bloggers highlight their 50th post. But, 171?

What's wrong with 171 anyhow?

We impose a psychological order on the world that is not really there. Number is a great example of that. Numbers are a mathematical construct. To get the entire set of whole numbers, you just need to define zero and a procedure for adding one to the previous number. After that, every number is as good as every other number.

Yet, our perception of numbers is affected by our experience with them. A classic paper by Sharon Armstrong, Lila Gleitman and Henry Gleitman from a 1983 issue of Cognition points out that round numbers like 100 are considered better examples of numbers than less frequently noticed numbers like 101, 99, or even 171. We focus on these round numbers. We think that they are more typical examples of numbers. We recognize them faster. We generally think of them as better numbers than less typical numbers.

The system of numbers doesn't play favorites, but the psychology of numbers does.

We also use our knowledge about round numbers to communicate precision to other people. If somebody tells you that an event happened 10 years ago, then you assume they mean a number in the neighborhood of 10. It might have been 9 or 11, but probably not 20. But if someone tells you that an event happened 11 years ago, you believe they are communicating something more precise. By using a less typical number, she is communicating greater precision.

A 100 sign

Finally, this focus on round numbers gives us a reason to mark landmarks in our lives by those numbers. We measure the performance of new Presidents by the activity in their first 100 days in office. We go to class reunions after 10, 20, or 25 years.

In fact, many of the days, weeks, and years in between landmarks may feel like a blur. We mark landmarks in time like birthdays and anniversaries as a way of remembering what we have done in that time period. They make the passing months and years more memorable.

The round numbers serve a similar function. We use the "good" numbers as milestones for marking large passages of time. Recognizing that 20 years have passed since a graduation or that you have been married for 10 years or that you have been working for a company for 20 years allows you to think through all that you have accomplished in that time. It is also an opportunity to take stock and think about what you would like to do differently in the future.

Which isn't to say that you can't celebrate other numbers as well.