As, like, as if, as though

Let's compare these two sentences:
Helen works as a teacher in a local school.
Helen works like a dog all day.
The first sentence tells us that Mary is a teacher. The second one compares her to a dog, but she is not a dog! So, we use as to say what the job, function or role of a person is, whereas like is used for comparison.

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As can also be used for comparison, but it must be followed by:

• A clause (Subject+Verb): She makes the cakes as her mother used to make them.
• A prepositional phrase: In London, as in New York, there is too much traffic.

Like is used for comparison but it's always followed by a noun or noun phrase, not by a clause. However, in colloquial English you can hear it in cases in which as should be used. Although not considered correct, it seems that this trend is getting more and more common these days, and might become the rule in the future. Who knows?
This usage of like is very common in songs, which use colloquial expressions and even slang. This song by RIO titled "Like I love you" is a good example.

As must be used after the expressions the same and such:
When I arrived at the party, another woman was wearing the same dress as me!
We can do many things to help the environment, such as recycling, saving energy and using public transport.

As is also used in expressions such as as expected, as requested, as you know, as we agreed, as suggested,... Again, like can be heard in some of these expressions, but bear in mind that it's colloquial English.
Finally, as is used in the comparative of equality, as we saw in a previous blog post. Let's remember some of the idioms we saw in this presentation:


With the verbs of the senses (look, feel, taste, smell and sound) we can use like and as if or as though. (The last two are the same). You only have to take into account that like is followed by a noun or noun phrase and as if, as though are followed by a clause.

• Your brother looks like a rugby player. (noun phrase)
• You look as if you haven't slept for ages! (clause: Subject + Verb)
• You are so pale! You look as though you had seen a ghost! (clause: Subject + Verb).

When the verb in the clause is in the past, the comparison is unreal or improbable. In the last example above, it's clear that the person has not seen a ghost, it's just a comparison. However, in the second sentence (with a present tense verb) there's a strong probability that the person has not slept for a very long time. 

Please, note that the verbs of the senses can also be followed directly by an adjective:

These shoes feel comfortable.

What are you cooking? It smells delicious!

You look tired.
It sounds familiar to me.

It smells delicious!
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And now, some exercises:
As or like?
As, like or as if / as though?