Expression "keep [verb]ing" in past continuous

Question

Let us take the following sentence:

You keep saying that I'm too young!

What is the grammatical equivalent in the past continuous? Given that "keep" is a verb, it should be okay to conjugate it, so I would say:

You were keeping saying that I was too young, but recently you changed your mind.

My girlfriend, however, thinks that, as it is an expression, you need to keep it to its initial form:

You were keep saying that I was too young, but recently you changed your mind.

Who is right between the two of us? And if no one is, then what is the right way of using the expression "keep + [verb]-ing" when talking in the past continuous?

Answer 1

The construction you're looking for just puts KEEP in the past-tense form:

You kept saying I was too young.

We don't ordinarily cast the idiom KEEP VERBing in the continuous (progressive) construction—I don't think I've ever encountered that. The reason is fairly obvious: KEEP VERBing is inherently continuous, expressing in itself the same notion of "continue indefinitely" which the continuous construction expresses, so casting it in the continuous construction wouldn't add any shade of meaning.

A secondary reason for avoiding the continuous with this idiom is that the collocation of two -ing forms (keeping VERBing) is unpleasant under the horror aequi principle:

... the widespread (and presumably universal) tendency to avoid the repetition of identical and adjacent grammatical elements and structures. — Gunter Rohdenburg, “Cognitive complexity and horror aequi as factors determining the use of interrogative clause linkers in English”, in Rohdenburg and B. Mondorf, Determinants of Grammatical Variation in English, 2003.