As and Like

As

1. 'As' may mean 'because'.

• As it was raining, we stayed at home.

2. 'As' may mean 'while' or 'at the same time':

• As I was walking down the street, I saw Marina.

3. 'As' expresses the way in which one thing resembles another. Here too it functions as a conjunction and must be followed by a subject and a verb, or by a prepositional phrase. In formal style the subject and verb are sometimes inverted.

• Daniel loves spicy food, as I do (or 'as do I', more formally).

4. 'As' is required in expressions such as 'as much as' and 'as + adjective + as', which likewise express similarity. These may be followed by a subject and a verb, or by a noun or preposition.

• Daniel loves spicy food as much as I do.
• Elena travels as much as me.
• She's as clever as her sister is.
• London's not as big as Mexico City.

5. 'As' combines with a noun to indicate a person's position, most commonly their occupation. In the same way it indicates the function of a thing, that is, what it is being used for. A noun must follow.

• She works as a teacher.
• Don't use the knife as a screwdriver.

Note that 'like' cannot express a person's actual occupation. 'As' is required.

• I work like a waitress.

Like

1. 'Like' introduces examples. It is equivalent to 'for example' and is normally followed by a noun or pronoun.

• I love big cats, like lions.
• Western European countries like France and Spain have high unemployment at the moment.

2. 'Like' also expresses resemblance between one thing and another. Here it functions as a preposition and is followed by a noun or pronoun.

• Daniel loves spicy food, like me.
• Tokyo is a busy and exciting city, like London.

In expressing resemblance, 'like' commonly accompanies verbs such as 'look', 'sound' and 'smell'.

• She looks like her mother.
• It looks like rain.
• That sounds like a car.
• The kitchen smells like lemons.

Traditionally, 'like' had to be followed by a noun. In contemporary English it frequently serves as a conjunction and is followed by a subject and a verb. Some regard this as incorrect, but it is extremely common.

• Daniel loves spicy food, like I do.

'Like' vs 'as' for similarity

Both 'as' and 'like' are often available for expressing similarity.

• I love coffee, like Marina / I love coffee, like Marina does.
• I love coffee, as Marina does.

'As' must be followed by a clause containing a subject and a verb. In this use it does not take a noun or pronoun.

• I love coffee, as Marina.

Where 'as' denotes a role or occupation, and is therefore followed by a noun, 'like' cannot replace it. 'Like' expresses resemblance instead.

• As your mother, I'm telling you not to go out now. (I am your mother, and I speak in that capacity.)
• Like your mother, I'm telling you not to go out now. (I am not your mother, but I am saying what she says, and acting as she would.)

A further example:

• She works as the manager (= she is the manager).
• She works like the manager (= she is not the manager, but works in a similar manner).