on to

on to, onto

On to is recorded in continuous use as a complex preposition from the late 16c, and the one-word form onto from the early 18c. In modern use both forms are found; onto has become more common in recent years but has still not achieved the dominance enjoyed by into (which goes back to Old English):

• French windows opened from the breakfast-room on to the terrace and large walled garden —Penelope Lively, 1981

• The blue sky threw its light down onto the fields below —L. Norfolk, 1991.

Note that in some uses on is used as a full adverb and needs to be spelt separately: They drove onto the beach means ‘they parked the car on the beach’, whereas They drove on to the beach (with the sentence falling into two parts between on and to) means ‘they continued their journey until they reached the beach’. Care also needs to be taken to retain the identity of on in phrasal verbs when these are followed by to: It was some time before she cottoned on to what he meant.