I noticed a common error during a few of my classes recently, so I decided to write about it. People make this error because there are different ways to join clauses with so and because. In each case, there is a reason (cause) and a result (effect). Sometimes the resulting sentences are very similar in meaning, but they can also mean the opposite of what was intended. Let’s look at it.

The word because indicates that a reason is being expressed. Notice that the reason always follows the word because:

Because the weather was beautiful
Because I have an exam tomorrow
Because it may rain tomorrow

The word so has different uses, but one use is to express a result or effect.  Notice that the result always follows the word so:

so we went on a picnic
so I am studying
so she’ll carry an umbrella

Reasons are always reasons for something.  They answer the question why?  Likewise, results always follow some event or idea. 
Consider the two clauses:

 I have an exam tomorrow.
I am studying.

These clauses are obviously related.  A writer may want to emphasize this relationship by joining these clauses into one sentence.  Great idea!  But this is sometimes where the problem begins:  

I have an exam tomorrow, so I am studying.
I have an exam tomorrow because I am studying.

The first sentence is correct.  I am studying is the result, and results come after so.  What comes after because?  Reasons do.  So which clause above should come after the word because?  Think about it.  Reasons answer the question why?  Which makes more sense?  

Why do I have an exam?  Because I am studying.
Why am I studying?  Because I have an exam.

The reason seems to be that I have an exam.  The idea is that if I didn’t have an exam tomorrow, I might be doing something else like watching TV,  chatting with my friends, or sleeping.  Notice that these two sentences express pretty much the same thing:

I have an exam tomorrow, so I am studying.
I am studying because I have an exam tomorrow.

You might say that the sentence with so emphasizes the result and the sentence with because emphasizes the reason.  But in both sentences , the reason for studying is that I have an exam tomorrow.  Notice that while the reason comes after because, it always comes before so. 
Finally, the sentence with because can be expressed in two ways:

I am studying because I have an exam tomorrow.
Because I have an exam tomorrow, I am studying.

I didn’t just move the word because to the beginning of the sentence:  I moved the because clause to the beginning of the sentence, and I put a comma after it.  So, you can choose how to express reason and result and which to emphasize.  It is completely up to you.  But there is another error to beware of.

Best of Both Worlds

Sometimes a learner will use both because and so in the same sentence instead of choosing one.  

Because the weather was beautiful, so we went on a picnic.

Here, the placement of the reason is correct:  after because/ before so.  But you have to choose one or the other (unless you have more than two clauses).  Don’t be greedy:

Because the weather was beautiful, we went on a picnic.
The weather was beautiful, so we went on a picnic.
We went on a picnic because the weather was beautiful.

Pretty straightforward?  Now you try it.   How would you join these sentences using so and because?

She wanted to relax.
She had a day off.

The dog next door was barking.
She couldn’t sleep.

She decided to go for a walk in the park.
The weather was beautiful.

You know how to express reasons and results, so write and speak with confidence.