Five Uses of "So" in English

Although it is a very tiny word, "so" has many different uses in English. In fact, "so" can take on three completely different roles: it can be an interjection, an adverb, or a conjunction, and as a conjunction it can introduce two very different types of clauses, purpose and result. The information below should help you sort out these common uses of "so" in English, along with the punctuation rules that go with each one.


1. SO (interjection). The word "so" is often used as an interjection, providing a kind of loose introduction to the sentence that does not convey a specific meaning. Instead, it just signals a nice and easy transition to get the sentence going:

• "So, you are telling me to work hard like you, Mister Ant, is that it?" asked the grasshopper.

As with any interjection, you need a comma to separate the interjection from the rest of the sentence. (Here is more information about interjections.)


2. SO (adverb) = ALSO. You can use "so" in a sentence with the same meaning as "also, likewise, similarly."

• The ant is a tiny insect, and so is the grasshopper.

3. SO (adverb) + adjective (THAT). A very common use of "so" is to intensify an adjective or an adverb. Here is an example with an adjective:

• The summer sun is so hot!

This type of statement is often followed by a "that" clause which expresses the consequences of the statement. You do not need a comma in a so ... that sentence:

• The summer sun is so hot that the grasshopper rests in the shade instead of working.

Here is an example with an adverb:

• During the summer, the ant gathers food so diligently that he has enough to last all winter.

(You can use the word "such" in a very similar type of construction: The ant is such a hard worker that he works even on the hottest days of summer.)


4. SO = conjunction introducing purpose clause. You can use "so" to begin a purpose clause that expresses the reason why something is done, the purpose of some action. When the "so" clause expresses purpose, you do not need a comma:

• The ant gathers food in the summer so he will have enough food for the winter.

To see if you are dealing with a purpose clause, replace "so" with the words "on purpose so that" and see if you get the right meaning: The ant gathers food in the summer (on purpose) so (that) he will have enough food for the winter.


5. SO = conjunction introducing result clause. You can also use "so" to begin a result clause, expressing the consequences of some action. This construction DOES require a comma:

• The grasshopper did not gather food in summer, so he did not have anything to eat in winter.

To see if you are dealing with a result clause, replace "so" with the words "so as a result" and see if you get the right meaning: The grasshopper did not gather food in summer, so (as a result) he did not have anything to eat in winter.

The comma here is very important! That is how you tell the difference between a "so" purpose clause and a "so" result clause: the purpose clause does not have a comma, but the result clause does. The presence or absence of the comma changes the meaning of the sentence.


SUMMARY: If you are using "so" as an interjection at the beginning of a sentence, you need a comma, and you also need a comma if "so" is introducing a result clause. The other uses of "so" in English do not require a comma.

(illustration by John Rae)