¿Cuál es la diferencia entre 彼女は学生で日本語を勉強していた y 彼女は学生でしたが、日本語を勉強していた ?Puedes dar oraciones como ejemplo.

She was a student, was studying Japanese and is very beautiful.
When the predicate describes a state (i.e. an adjective, a noun, a verb which doesn't have the continuous form ている/ていた) and is followed by a verb which has the continuous form, it doesn't change its meaning whether the verb is in the continuous form or not. e.g.

1)彼女は学生で日本語を勉強していた/ 1.1)彼女は学生でしたが、日本語を勉強していた She was a student and was studying Japanese


2)彼女は学生で日本語を勉強した/ 2.1)彼女は学生でしたが、日本語を勉強した She was a student and studied Japanese

In both sentences (1,2) the first bit is translated into "she was a student" regardless of whether the last verb has the continuous form or not.


3)彼女は学生で日本語を勉強している/ 3.1)彼女は学生ですが、日本語を勉強している She is a student and is studying Japanese/ studies Japanese

4)彼女は学生で日本語を勉強する/ 4.1)彼女は学生ですが、日本語を勉強する She is a student and studies Japanese/ will study Japanese

In both sentences (3,4) the first bit is translated into "she is a student" regardless of whether the last verb has the continuous form or not.

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Also, I noticed Japanese uses the particle が to connect predicates with different temporal aspects as in the sentence


彼女は学生で日本語を勉強していたが、とてもきれいだ。She was a student, was studying Japanese and is very beautiful.

so I added those versions (1.1,2.1,3.1,4.1) as well. What do you think the difference between 彼女は学生で日本語を勉強していた and 彼女は学生でしたが、日本語を勉強していた is? Assuming that what I wrote so far is correct (which I don't think is the case)