Many people wonder when they should use ‘on’, ‘onto’, and ‘on to’. Here are some simplified guidelines for them.
‘On’ is a preposition that means the subject of the sentence touching and being supported by the top surface of (something).
For example, The book is on the table. this sentence suggests the book is already there.
On the other hand “onto” is a preposition that suggests movement.
For example, The dog climbed onto the sofa. This means that the dog was not on the sofa at first. He climbed there.
Another way to use “onto” is as a phrasal verb. Being onto somebody or something means knowing about something or someone else’s situation(especially if they have done something wrong).
For example, The cyber police are onto the hackers. This means the police know about the hackers’ crimes.
There is another less common use of ‘onto’ in speech but very rarely in writing. The word ‘onto’ can refer to a transition or continuation from one action to the next.
For example, I’ll go onto the next question after I finish this one.
There’s a situation in which ‘on to’ can be used rather than ‘onto’. Because they don’t go together at all, the space between the ‘on’ and the ‘to’ serves to separate them. The word ‘on’ is part of a phrasal verb and ‘to’ is the preposition.
For example, I will log on to the computer. here the word ‘log on’ is a phrasal verb and ‘to’ is the preposition.