Both Dana and Ardis are correct in their respective statements.
This is because a difference of two vectors can always be represented as the sum of a positive vector and a "negative" vector. (Please note that a negative vector is a vector whose direction has been turned [tex] 180^0 [/tex] or has been made "opposite".)
The following explanation will further clarify.
Let us say [tex] \underset{A}{\rightarrow} [/tex] and [tex] \underset{B}{\rightarrow} [/tex] are two vectors. Then the difference of the two vectors can be represented as:
[tex] \underset{R}{\rightarrow} = \underset{A}{\rightarrow}+(-\underset{B}{\rightarrow}) [/tex] (where [tex] \underset{R}{\rightarrow} [/tex] is the resultant vector).
Thus, as we can see a difference of two vectors can be thought of as the sum of two vectors.
