The weather is changing.
This sentence is an active voice sentence and in active voice sentences the subject is a “doer”. So, I want to know that what is the subject in this sentence?
If weather is the subject then it should be doer. So, the above sentence would mean that weather is changing something but then the question arises that what can weather change?
And if the weather is being changed, then who is changing the weather?
Not all verbs need an object. Change can take an object, but it does not need one.
Compare the transitive:
John has changed his house. He redecorated it.
with the intransitive:
John has changed. Becoming a father made him mature.
So you do not need a object with change. Something or someone can change, meaning that they become (something) different.
In your sentence, the weather is indeed the "doer". But the weather cannot do something!
We use a lot of expressions where inanimate objects do things:
The door is closing.
The suspense is killing me!
In The weather changed, the verb change is being used intransitively. That means it does not take a direct object.
Change can also be used transitively as in I just changed a wheel on the car.
In general use, the current weather conditions are becoming different. Perhaps the temperature is dropping or it has begun (or stopped) raining.
This phrase might also be used in a discussion about global warming, which would mean a broader time frame. "The weather is changing, summers are becoming hotter and the ice caps are melting."
In this sentence "changing" is used as a reflexive verb with drop of the reflexive pronoun as it often occurs in English.
