This question already has an answer here:
- “To your left” versus “on your left” 2 answers
John entered the hall. On/to his left was a table.
John saw that to/on his left was a table.
On Google, I found more results with "to", but I guess that doesn't make "on" wrong. To my ear, "on" refers to a more generic position, and closer to the subject, whereas "to" refers to a precise direction, that might be very distant. Another example:
On/to his left was a mountain.
To me "on" sounds like the mountain is closer, almost towering the subject. "To" instead make the mountain farther from him. Am I correct? If not, what are the differences? In which contexts one is preferable over the other?