Subsetting data.table column through a variable list

Question

I have the following data.table:

dt<- data.table(V1=c(1L,2L),
                V2=LETTERS[1:3],
                V3=1:12)

I want to subset the first and second columns like this:

dt2 <- dt[, c("V1", "V2")]

Works fine. However, when trying...

chosen.cols <- c("V1", "V2")
dt[,(chosen.cols),with = F]

... it only works appending the 'with=F', otherwise it returns:

[1] "V1" "V2"

1) Why do we need 'with ='?

2) What exactly 'with =' implies to the code?

Thank you.