Like vs. As

Like and As are used to indicate that something is similar to other thing .The two have similarities and distinctions:

1- Grammatically, like is used as both preposition and adverb to give examples and is followed by:
a-A noun or pronoun as a preposition 

- South American countries like Peru, Colombia and Brazil tried to establish…

- Flowers like rose, require special care.

- Various trees, like oak or pine

b-A gerund (-ing form of the verb, used as a noun), or a noun clause:

- He has a lot of hobbies, like painting, skiing.

Notice that such as and as can be used instead of like in the above contexts. Although in various dictionaries such as the freedictionary.com ,dictionary.com and Merriam -Webster.com, it has been mentioned that as can be used as an adverb instead of like in the above sentences , practically, the word is not recommended in many grammar books and generally it is not very common in this use.

c- A noun or adjective meaning In the manner of being; as if. Used as an intensifier of action:

- Worked like hell; Ran like crazy. We'll have to run like the wind.

As can not be used in this case.


Like is used to indicate the comparisons of two or several things:

- A man like him can be the ideal person for the position.(Not a man AS him…)

- My car is not like your car.(Not My car is not AS your car)

- Her hair is dark brown like mine.(Not Her hair is dark brown as mine)

Using As and Like as conjunctions

2- As is used as a conjunction and introduces a subordinate clause (a clause contains a verb); so it can be used:
A- Before a clause:

- Nobody can speak English in the class as he does.

- They don’t know the new boss as I do.

- They often take a nap after lunch, as we do in Iran

- He is not good at French, as I am.

Like can be used as a preposition which is only followed by an object or pronoun:

- Nobody can speak English in the class like him.

- They don’t know the new boss like me.

- They often take a nap after lunch, like us in Iran.

- He is not good at French, like me.

 like in this use is only limited to casual or conversational English, but they're not grammatically correct .

Like is used in informal style as a conjunction and is more common than as in this case:

- Nobody can speak English in the class like he does.

- They don’t know the new boss like I do.

- They often take a nap after lunch, like we do in Iran

- He is not good at French, like I am.

Grammatically sticking, This use of like is considered wrong because like only can be used as a preposition but many believe that this kind of use of like is getting more common and acceptable as a conjunction in informal English.

B- Before an expression(usually time or place) beginning with a preposition:

- This weekend as in last weekend we are going to go skiing

-There is too much traffic in London as in New York.

- In 1994 as in 1995 he made a great fortune in his business.

 In this use like can be used instead of as .

In meaning as is used to indicate that two things are equivalent, while like shows that they're similar. In other words, as is used to describe that someone/something has a particular job or function.

Like is used as a preposition to imply that something or someone is in like manner with; similarly to; in the manner characteristic of

Compare the following sentences:

a) He treated Mary as a friend.

(He was the friend of Mary)

b) He treated Mary like a friend.
(He was not the friend of Mary but treated her in a way that everyone may have thought Mary was his friend. Mary here has simply been compared to a friend)

3- Like as an adverb means in the same way as; as in this sense can replace with like:

- It happened like/as you might expect it would.

- Make the cake like/as you did last week.

- I'll help her like/as I would help anyone.

Like, though, is used informally in these sentences. It would also be correct in this sentence.