We can use like or as to say that things are similar.
- She is like her sister.
- He is a doctor like his father.
- Like his brother, he is a vegetarian.
- You are dressed just like me.
- He fought like a tiger.
Like is a preposition. It is used before a noun or a pronoun which acts as its object.
As is a conjunction. It is used before a clause or an expression beginning with a preposition.
- Nobody loves her as I do. (NOT Nobody loves her like I do.)
- In 1939, as in 1914, everybody seemed to want war.
- He fought as a tiger does.
Informal use of like
In informal English like is often used a conjunction instead of as. This is very common in American English.
- Nobody loves her like I do.
Comparison with as and like after negatives
Note the word order in the following sentences.
- I don’t sing, like Jane. (Jane sings, but I don’t.)
- Like Jane, I don’t sing. (Jane doesn’t sing; neither do I.)
- I am not a Catholic, like Mary. (Mary is a Catholic, but I am not.)
- Like Mary, I am not a Catholic. (Mary is not a Catholic; nor am I.)