Parallelism

[WendyH75]

If the sentence structure is..... sth happened and therefore resulting in sth else

ie. The flood destroyed the plants and therefore prices rose. Does the parallelism rule still apply ( X AND Y) when there is a transition word added between the AND and the Y component?

[Sage Pearce-Higgins]

You're right that 'and' is used in more than one way. In the example you gave, it's simply joining two potentially complete sentences together. As much as we'd expect a connection in meaning, these two parts of the sentence don't need to be parallel. Your example seems fine. The presence of the word 'therefore' doesn't make much difference to parallelism here. The "X and Y" parallel construction that you refer to is something more like 'I bought apples and bananas.'

It's worth thinking, however, exactly what we mean by 'parallel'. It doesn't mean that everything has to be exactly the same kind of word. Check out the Parallelism chapter in the SC strategy guide for more on this.