stop somebody from doing something
Why should we use the preposition "from" here? What is it for? Why not use "stop somebody to do something"? This really confused me.
Learn English – The usage of “from” in “stop somebody from doing something”
prepositionsword-usage
Best Answer
In many cases, there's not really a reason why we use one preposition rather than another. In this case, though, I'd say we use from because it conveys a sense of away, apart, separate (you're keeping the person and the action "apart").
But note that we don't need to use a preposition at all - "She sang a lullaby and stopped the baby crying" is fine (as is "...stopped the baby from crying"). Also note that in related constructions like "She helped the baby to eat", "to" isn't a preposition as such - it's just the "marker" for the infinitive verb form "to eat".
And while we're on the subject, I'll also say that in "She sang the baby to sleep", the preposition "to" seems quite "rational" to me because it reflects "movement" from wakefulness to, towards sleep.