Onto and on to are prepositions that sound alike, but they are different in form (the former is one word and the latter is two words). Moreover, you can’t use them in the same situations. You use “onto” when referring to movement, understanding or awareness of a situation, and transition. Meanwhile, you use “on to” when the preposition “on” is part of the verb.
When to Use Onto
You commonly use “onto” when something or someone has moved, is moving, or will move to a position on another surface, area, or object. It has the same meaning as “upon” or “on top of.” Mainly, it is used when describing a level of change in the movement of animals and people.
The dog jumped onto my lap. It’s so cute.
Please put that box onto the cabinet so the cat won’t reach it.
I saw him walk onto the platform during the ceremony.
You use “onto” when showing understanding of a concept or awareness of a situation. It shows that someone is “fully aware of” or “informed about” something.
The girl was onto the magician and stopped believing his tricks.
Elle thinks that the guy is up to something fishy. She’s onto his actions.
They tried to surprise me for my birthday, but I was onto their plan when I saw the balloons and decorations.
Indicating Transition or Continuation
You use “onto” to indicate a transition or continuation from one activity to another. It’s mostly used in speech, but rarely used in writing.
I’m done with the hardest task. Onto the next!
I finished decluttering my cabinet, and now I’m onto the drawer.
We had a tiring day finishing our project. Onto the next day!
When to Use On to
Using “On” as Part of the Verb
You use “on to” as two words, one that has space between the words, when the verb includes “on.” This is called a phrasal verb — it’s the combination of a verb and a preposition or an adverb to create a particular meaning. Check helpful grammar resources to learn more about phrasal verbs.
Pour the toppings on to the cake.
(pour on is a phrasal verb)
You need to log on to the computer to fix the bug.
(log on is a phrasal verb)
Go on to the next page.
(go on is a phrasal verb)
After going to the art museum, we moved on to the science museum.
(move on is a phrasal verb)
Conclusion: Onto or On to
Onto and on to are two different prepositions. Generally, onto implies movement while on to are two words, and when paired with each other, on acts as a part of a phrasal verb and to acts as a preposition. If you’re confused with phrasal verbs, use reliable grammar tools, a grammar checker, or even an AI writing tool.
If you’re unsure if it’s “onto” or “on to,” always look for context. Use “on to” when “on” belongs to a verb phrase and use “onto” if you’re showing that something or someone is being positioned on top of something else.
Cambridge Dictionary. (n.d). Onto. In https://dictionary.cambridge.org/ dictionary. Retrieved Jan 26, 2022, from https://dictionary.cambridge.org/dictionary/english/onto
Longman Dictionary. (n.d.). Onto. In https://www.ldoceonline.com/ dictionary. Retrieved Jan 26, 2022, from https://www.ldoceonline.com/dictionary/onto
Martinet, A.V., Thomson, A.J., A Practical English Grammar 4th Edition. Oxford University Press. p 95.
Swan, M. Practical English Usage 2nd Edition. Oxford University Press. p 269.