- The hen got happy.
- The hen became happy.
Which verb should I use between got and become? And Why?
I don't find either got happy or became happy to be particularly natural. I would simply use was happy, and leave whether that is an observation or a contrast with a previous state to be understood from context:
She had been irritable all through dinner, but now that the stag's obnoxious friends had departed, the hen was happy.
Leaving that aside, it is true that some meanings of the extremely versatile get mean become, specifically:
- Reach or cause to reach a specified state or condition
[ODO] Worth noting is the usage note:
The verb get is in the top five of the most common verbs in the English language. Nevertheless, there is still a feeling that almost any use containing get is somewhat informal. No general informal label has been applied to this dictionary entry, but in formal writing it is worth bearing this reservation in mind.
In other words, get happy would be more common in conversation and in informal writing, whereas become happy would be more acceptable in formal registers. That is broad a generalization, but it has usage implications.
Get has a somewhat greater connotation of agency or intent, perhaps because many of its other meanings are causative, and refer to inducement, deliberate movement, or inflicting injury or punishment. If I say I got drunk on cough syrup, I may be interpreted as intentionally drinking cough syrup to get drunk. If I say I became drunk on cough syrup, I am distancing myself from the act, saying the drunkenness was unintentional.
Become being more distant and thus "softer," it is much rarer as an imperative, in verbal communication or informal writing. Get is more direct, whether you want to be forceful— Get ready! Get cracking! Get out!— or more personal— Get well soon!
For additional usage notes, BBC Learning English has a unit on 'Get' and 'become'. At EL&U see Is “get” (in the sense of “become/make”) appropriate for formal writing? and He was getting vs being beaten among others.
Note also that get is involved in a large number of idioms, some vulgar. If John and Mary are lollygagging around the office, their manager must be careful about saying The two of you should get busy as that can be taken to mean that they should have sexual relations. Similarly, get happy to Americans is more likely to be taken to mean getting drunk or high on marijuana than as a reference to a Judy Garland song (which was probably performed by a Judy Garland who was both).