• 3-minute read
• 14th November 2017

Know Your Prepositions! (As, At and By)

Picking the right preposition can be tricky. After all, there are so many to choose from! But prepositions can make a big difference to the meaning of a sentence, so it’s important to know how these terms work if you want to avoid grammatical errors in your writing.

Here, then, we look more closely at three common terms: ‘as’, ‘at’ and ‘by’.

As (Function and Character)

The word ‘as’ has many functions. In fact, it isn’t even a preposition most of the time! Usually, it is either an adverb (when making comparisons) or a conjunction (when linking clauses in a sentence).

However, it can also be a preposition, where it always comes before a noun. In this case, it is used to express the function or character of something:

Monique works as a proofreader.

Alan was difficult as a child.

In the first sentence above, ‘as’ points to the type of work Monique does. In the second, ‘as’ tells us the time (and state of being) during which Alan was difficult.

At (Location, Position and State)

The good news is that ‘at’ is always a preposition, so on that level it is simpler than ‘as’. Unfortunately, it also has many uses as a preposition, so it is still tricky!

We won’t list all of its functions here, but some of the most important include showing:

• A location (e.g. They will be at the party later)
• When something takes place (e.g. We will get there at 8pm)
• A point on a scale or in a process (e.g. We’re at the halfway point)
• A state or condition (e.g. I’m good at cricket)
• The object of an action or attention (e.g. He keeps staring at the clock)

Most of the time, then, ‘at’ indicates a location, position or state of some kind.

By (Responsibility and Means)

Finally, we have ‘by’, which is almost always a preposition. This term has many uses, too. Nevertheless, we can summarise some of the most common, which include indicating:

• Who performed an action (e.g. The goal was scored by Viduka)
• The means by which something was done (e.g. I travelled by bus)
• The size or amount of a difference (e.g. We improved output by 25%)
• A deadline or the end of a period of time (e.g. We need it finished by Tuesday)
• That something is next to something (e.g. She found it by the side of the road)
• The period during which something happens (e.g. Most owls hunt by night)

As with ‘at’, the variety of uses here can seem confusing. But if you keep the definitions above in mind, and practise using different prepositions, you should get the hang of them in no time!