I'm quoting the definition of Resultant of two forces acting in the same line from the book "A FIRST COURSE IN PHYSICS" one of whose authors is Robert Andrews Millikan:
The resultant of two forces is defined as that single force which will produce the same effect upon a body as is produced by the joint action of the two forces.
I'm really confused as to whether the resultant of two forces say $A$ and $B$ is the force which is produced as a result of the two forces just mentioned or is it a completely separate force which is not caused by $A$ and $B$, but its effect is the same as that of the force produced as a result of $A$ and $B$? Even though, the force caused by $A$ and $B$, let's say it is $C$, is equal in magnitude to that of the resultant $R$ of $A$ and $B$ and the direction is also the same, but $C$ is caused by $A$ and $B$; however, $R$ has no primary causes as $C$ has. This is what I conclude from this definition; however, I'm not sure yet.