fill in
I cannot fathon why " fill in " is correct in the two following sentences
fill in a form
fill in your personal information in the chart
I mean why can it be followed by "what you use to fill something in " and by "the thing you fill in"?
Thank you very much
An interesting question!
I think you will find English has many similar peculiarities.
I am not sure of the exact grammatical explanation, but "fill in a form" and
"fill in your personal information" both sound correct.