(I'm sure Cubdriver will jump in and fine-tune anything I may have clouded).

Actually, it doesn't have to be aerodynamically unstable...this could be done with conventional controls, but probably won't.

1. Conventional aft-swept wings have a span-wise flow, which means the air doesn't go straight back with the freesteam..it goes outboard a little. This causes a local increase in angle of attack, the farther it goes, and makes the tips of the wing stall first. It is the reason most swept-wing jets have aerodynamic twist or "washout," where the chord of the airfoil goes more nose-down as you move outboard.

Since the flow goes outboard, vortices are stronger. Vortices are a loss of high-energy air, and a source of drag.

With forward-sweep, the spanwise flow goes inboard. That high-energy air is trapped under the wingroot or fuselage, and does useful lift....which reduces drag, and therefore, power required, and therefore, cost of operation.

2. Canards are lifting surfaces, as opposed to conventional horizontal surfaces. A conventional tail puts a downforce on the aircraft, which increases the total load the wing must lift....more cost of operation.

The big disadvantages of FSW:

1. Since spanwise flow is at the rear-most part of the wing, and local increase in AOA happens there, it will stall root-first. Since this is the aftmost part of the wing, a stall causes a nose-up pitch...generally the opposite of what you want.

2. FS Wings are aero-elastically unstable. That is, bending loads from lift and drag want to bend the wing backwards and upward....which causes an increase in AOA unless the wing is hugely stiff and strong. The X-29 used a carbon composite wing to address this issue. In the end, the manufacturers apparently felt that not enough performance was gained in a fighter for the weight penalty that had to be paid.

Disadvantage of canards:

The adavantage of the canard is it reduces the amount of load on the wing, instead of adding to it like a horizontal stabilizer.

I read a discussion of the Sonic Cruiser where airline reps wondered how airport gates would have to be configured for the jet bridge to clear the canard, or insure that a malfunctioning jet bridge (gee, that's never happened), or clumsy/barely trained operator (hmmmm) doesn't damage the aircraft.

Interesting point.

It is an intriguing design. I see it as trying to reduce drag and thereby reduce fuel cost. The article said it would make it quiet...I doubt it, at least for passengers. Not much different than a 727 or DC/MD. The vertical fins might make a difference for noise footprint on the ground, though.