Fictitious Forces $\overset{?}{⇔}$ Constraint Forces (re: D'Alembert's Principle) Are fictitious forces and constraint forces the same thing?
 A: There are not the same thing. Fictitious forces usually arise because of change of co-ordinates, e.g. to a rotating frame. They are terms added to make the whole equation look like a vector sum of forces. The constraint forces are very real, and arise due to geometrical constraints, such as motion along a plane gives rise to the normal force produced by the plane, or the constancy of the length of a string tied to a pendulum gives rise to the tension. 
A: The question is legitimate in the sense that one can often read, especially in older literature, that "d'Alembert's Principle has successfully reduced Dynamics to Statics". If d'Alembert's Principle (principle of virtual work) stated for a constrained system in equilibrium
$$ \sum_k{F_k\ \delta r_k =0}$$
is enough to lay the foundations of Statics (bridges, buildings) then it is a remarcable result that the very same principle would completely suffice for Dynamics. 
In this case then the $- m \dot  v $ addition to the principle are really nothing more than the fictitious forces appearing in the comoving frame where the representative point is at equilibrium (pure statics). 
