That would be "train of thought" not "thoughts", and they would be classed as collocations (or "word partnerships") if referring to this description.Originally Posted by Thinking
"collocation A term used to refer to the combination of words that have a certain mutual expectancy i.e. words regulary keep company with certain other words. When a collocation appears with a greater frequency than chance, then it is called a significant collocation. The usual measure of proximity is a maximum of four words intervening. "
I think the first two fit better into the category of fixed expressions, while "paper qualification" would suit the label "a collocation".
Remembering here what M Lewis said:
"Collocations co-occur, but not all words that co-occur are collocations."
- For Teachers