Learn English – “Got promoted” vs. “Was promoted”

Get is a very busy verb in English.

It's mostly an auxiliary verb, and it almost always is Inchoative in meaning -- i.e, it refers to a change of state, by referring to a state that is beginning.

Inchoative predicates (verbs and adjectives) often occur in sets of Stative, Inchoative, and Causative, which are often the same word, but sometimes not:

1. Stative predicate:
   The gate is open (wide)/(wide) open.
   The gate is closed (tight).
   The dog is dead.
   The dog is tired (out).
   He is (located) at X.
   They have (= possess) the book.
2. Inchoative predicate:
   The gate opened (wide).
   The gate closed (tight).
   The dog died.
   The dog tired. ~ The dog got tired (out).
   He came/went to X.
   They got (= received) the book.
3. Causative predicate:
   We opened the gate (wide).
   We closed the gate (tight).
   We killed the dog.
   We tired the dog (out).
   We brought/took him to X.
   They got (= acquired) the book.

Get is so busy because it's the inchoative of both the auxiliary verb be and the auxiliary verb have. And these auxiliary verbs participate in an awful lot of constructions. Therefore, so does get.

• Some examples of Inchoative uses of get (many idiomatic):
  

  • He was tired. ~ He got tired. (get = 'come to be')
  • He is moving. ~ He got moving.
  • He is married. ~ He got married.
  • He is being married. ~ He is getting married.
  • He is tired. ~ He got tired.
  • He has a cold. ~ He got a cold. (get = 'come to have')
  • He had it done. ~ He got it done.
  • He has the job. ~ He got the job.
  • He has to retire. ~ He has got to retire ~ He's gotta retire.

There is a valid literary technique that will subtly shift from past to present but it is much safer to pick one tense and stick with it.

An example of this device, which I copied from About.com's page on the subject:

Off the road there was what appeared to be a reviewing stand, and I sat there for a few moments, taking in the museum and the cold blue Sunday sky, taking stock, what to do, what to do next, I'd really hate to cancel dinner tonight . . . I'm breathing normally now, it's OK A-OK, I won't even tell my wife, nor Tim, especially not Tim, I feel fit as a fiddle now.

The page linked above has a handful of various thoughts and examples on the subject. It does explicitly note that we often do this sort of thing during informal speech:

What is an example of an unmotivated shift in tense in writing? One example is starting a story in past tense and suddenly shifting into present tense:

Last week I was walking along a street when this man walks up to me and says...

We do this in speech all the time, but in formal writing it's considered to be an error.

(Edward L. Smith and Stephen A. Bernhardt, Writing At Work: Professional Writing Skills for People on the Job. NTC Publishing, 1997)