The English language can be tricky. We have many pairs of words with similar meanings, e.g., “Each” and “Every,” “Some” and “Few,” and “Much” and “Many.” One pair that confuses many people is “In” and “On” when writing about when something happened.
Although I see native English speakers make this mistake, I most often see it from people whose native language is other than English. Native English speakers typically use these words correctly because they are accustomed to hearing them used correctly. Not so for people who didn’t grow up speaking English.
Let’s look at “in” and “on” and figure out which one to use.
Time can be divided into many types of time periods: months, years, days, hours, centuries, etc. Each time period has a beginning and an end. For example, if we write about the 20th century, we are writing about the time from January 1, 1900, to December 31, 1999. The century has a beginning and an end. If we write about the month of April, we are writing about the time beginning April 1 and ending April 30.
During a time period, something occurs. The time period begins prior to the event and ends after the event. The event doesn’t take up the entire time period. Rather than providing the exact date, we can refer to the time period. In these cases, we use the word “IN” to describe when the event occurred.
For example, let’s say the date of my birth was February 14, 1952. If I am writing about my birth, and I don’t want to give the exact date, I might refer only to the year. So, during the time period January 1, 1952, to December 31, 1952, I was born. The year began before my birth and ended after my birth.
In this case, I was born IN the year 1952. I’m not writing the specific date; instead, I am referring to the time period during which my birth occurred.
Here’s another example. February 14th is Valentine’s Day. However, if I am writing about Valentine’s Day and I don’t want to provide the exact date, I can write that Valentine’s Day occurs IN February. Valentine’s Day occurs during the time period called February, and I’m not providing the exact date, so I write “IN.”
Whereas “in” describes a time period, “on” provides the exact date. When we write “on,” we are not describing the time period during which the event occurs. Instead, we are communicating the specific date.
Using the examples above, I could write that I was born ON February 14, 1952. This is the specific date. Similarly, I could write that I was born on Valentine’s Day. This, too, refers to a specific day.
Now let’s look at the second example. When is Valentine’s Day? Valentine’s Day is February 14. That is the specific date ON which Valentine’s Day occurs. When we are writing about the date, we will use “ON,” as in Valentine’s Day is ON February 14.
The Main Difference
The main difference between “IN” and “ON” is this: “In” refers to a time period and is inexact. “ON” refers to a specific day and is exact.
Thus, I was born IN 1952, and I was born ON February 14, 1952.
A Joke to Help You Remember
Two men, Bob and John, were talking about all the things they have done in their lives. Bob asked John, “John, when was your birthday?”
John replied, “My birthday was ON December 12.”
“No,” said Bob. “I mean IN what year was your birthday.”
“IN every year!”
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