Fall or fall down?

We can use fall as a noun or a verb. It means ‘suddenly go down onto the ground or towards the ground unintentionally or accidentally’. It can also mean ‘come down from a higher position’. As a verb, it is irregular. Its past form is fell and its -ed form is fallen. Fall does not need an object:

Mrs McGrath had a terrible fall yesterday. She’s in hospital now. (noun)

Four trees fell in the storm. (verb)

Oil prices have fallen recently.

Fall down is a phrasal verb. We use it when something falls to the ground from its normal position:

The picture keeps falling down. (from the wall to the ground)

He slipped and fell down.

Warning:

We use fall, not fall down, when trees drop their leaves during the autumn:

As autumn came and the leaves fell from the trees, she began to feel sad.

Not: … the leaves fell down …

We can’t use fall down to mean ‘come down from a higher position’:

House prices have fallen a lot this year.

Not: House prices have fallen down a lot …