By or On

by on prepositions of time

'By' and 'on' may confuse the learners when it comes to referring to time. In this lesson, we will learn their differences and find out when to use them.

Which One Should Be Used?

Prepositions 'by' and 'on' are correct and can be used. We use 'by' to show that an event or action occurs not later than a specific time. We use 'on' to show and mark a specific point in time.

By

'By' is a preposition that helps show an era or a point in time at, before, or not later than a specific time. We commonly use it to set deadlines. For example:

By the time I got there, Nina had already fell asleep.

You have by midnight to email your assignments.

On

'On' is used as a preposition of time to show an exact point in time when something happened. It is mainly use to show days of the week, specific dates, and holidays. For example:

The meeting is on Monday.

Taylor used to throw parties on independence day.

Are They Interchangeable?

The answer is no. 'By' and 'on' show different time factors and replacing them will drastically affect the meaning and will confuse the audience. Have a look:

I will meet my parents on Christmas.

Here, the speaker will do the action on a specific day.

I will meet my parents by Christmas.

Here the speaker will do the action on some time before the said date.

Can They Be Used in One Sentence?

As they are showcasing points in time, we can use them in a sentence to give more details about the time of occurrence. Look at these examples for clarity:

She said she'll be here by midnight on May 12th.

See you on Saturday by 5 o'clock.