While many players embrace METHOD 1, some partnerships (notably Mechkstroth-Rodwell) prefer METHOD 2.

Fundamentally, we find partnership agreements fall in two camps:

On the side of the Scientists, in the Okbridge “Spectator” Marc Smith featured a series of Forcing Pass articles (6/01, 12/01, 1/02). Another Scientist, Eddie Kantar authored the definitive Forcing Pass book and wrote a series of articles for Bridge Today (2/05, 3/05, 5/05)

Scientists have more scenarios (and memory work) with less catch-all guidelines such as a universal “whenever opponents bid above our 3 Spade call and our bids are constructive, our subsequent pass is forcing.” Regardless of your approach, consider Environmental Factors – particularly vulnerability, freak distribution, and offensive/defensive tricks.

Here are several common situations:

When opener has near-game values such as a strong 2 Club opener showing 22+ points, many play a subsequent pass is a Forcing Bid; lacking a better bid, responder can double to keep the auction alive. However, when opener begins with a 2 Notrump bid showing 20-21 point, subsequent passes are not forcing.
 

Responder’s 2 Notrump bid is game-forcing so opener's pass is forcing. Note – see Jacoby 2 Notrump to review alternative methods after interference
 

Assuming you recognize responder’s 3S rebid as establishing a game force (opener jumps, responder rebids own suit), opener is making a Forcing Pass inviting responder to double or bid 4S with great Spades.
 

Here, opener can make a forcing bid by cuebidding opponents’ suit or calling a new suit. When opener (the stronger hand) bids a new suit at the 3 level, the call is invitational. Jumping in a new suit at the 4 level subsequently establishes a Forcing Pass if necessary. Opener’s jump to game has the same effect. Note: some play this treatment only with adverse vulnerability based on the risk-reward differential. At any rate, if opener takes another path, as rebidding at the 3 level, belated opener passes are not forcing. Note: many also play Maximal Doubles at the 3 level.

Yet rules like this one should not be thought of as iron-clad. Contrast these bids:

It is unlikely South is “walking the dog” with extra values on the above auctions. Apparently South is making a sacrifice bid so opener’s pass is definitely a Forcing Bid in these auctions. However, South may indeed be walking the dog on this auction:

The responder may be bidding game based on an anticipated double fit in the red suits after opener's Help Suit Game Try. Realizing this, opponent South may upgrade a two-suited black hand and solely bid game. Thus, the meaning of opener’s pass will vary by partnership agreement (again, some play forcing only with adverse vulnerability). As an aside, when your side bids a lower suit rank as Hearts over their Spades, it may not be wise to “advertise” a possible double fit – smart opponents certainly enjoy such useful information.

In some situations, the Scientists liberalize their conventional gadgets to replace the meaning of the Forcing Pass or even the double. Consider this auction:

Should a double be purely for penalty here, or is it a cooperative (optional) double asking partner to consider a 5H sacrifice with an offensive hand? Scientists point out the 1H overcall shows defensive values, not immediately making a preemptive jump to 4H. So a common treatment is “DSI”, asking partner to Do Something Intelligent! That is, “Partner, with defensive values of your own, let the double ride, otherwise think strongly about supporting my suit.”

So we've seen the Forcing Pass agreements can have many subtleties, particularly for the Scientists. Regardless of your approach, be sure your partnerships have clear agreements.

Finally, here's what the Bridge World Standard says about the Forcing Pass: