Are the Triple Constraints still useful?

Scope, Schedule, Cost – they are classics, but do they remain useful?. I’ve heard many practitioners call the Triple Constraints (TC) obsolete or, at least, inadequate.

Many PMs point out that we need to factor in quality. I don’t have a problem with this one. On the other hand, I didn’t know that Scope didn’t include quality. For me, Scope never meant just a list of things or features. Without a set of acceptance/quality criteria, Scope would be too fuzzy. So, with that proviso, I think Scope is still a good one.

What about Cost? I’ve had a lot of PMs tell me with an honest expression that they don’t think about costs because “they have to do it with what they have so it’s all fixed cost and so it doesn’t matter anyway.” Whoa. Maybe some of us forget that cost is really a measure of resources. For a lot of my projects, we were more focused on the hours/days of resources needed than on the $$. Even in a “fixed cost” environment, we will compete for resources – especially critical (in the sense of scarce) resources. If you don’t usually deal with the $ costs, let’s use Resources as the constraint. So, I think Resources is OK.

No one seems to question the importance of Schedule – except to say that the Schedule is always too short. Of course, if it is always too short, what does that say about either our estimation skills, or our assumptions about reality… but that’s for another time.

Another question is “Where’re the risks?” Clearly, risks are a critical consideration. For example, we may have a TC with a 10 month schedule. Examining risks, we find that we have a very low risk of missing the TC, but we have a significant risk being “left behind” a competitor with a significantly improved product coming in 6 months. If we want to reduce the competitive risks, we will have to rebalance the TC – perhaps by accepting a smaller Scope, or increasing Resources. in order to reduce the Schedule. So, maybe we have this:
triple constraints +
So, I’m still a fan of the Triple Constraints. Except now it’s the Quadruple Tetrahedron? I think Triple Constraints + Risk might be better.


4 thoughts on “Are the Triple Constraints still useful?”

  1. User Avatar

    I have heard many silicon valley high-tech PMs complain about ‘morale’ as a fourth side to the TC triangle. This is typically the result of death-march projects where great heroics are required by exempt employees to meet deadlines. Organizations that chronically rely on this process end up ‘depleting the fourth constraint’ and driving employees away due to low morale. This also usually results in higher hiring and training costs.


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    I’d like to meet some of the folks who actually feel that the triple constraints no longer matter, so they can explain their reasoning to me. The triad of


    covers every nuance. Yes, scope includes quality as well as feature set, and cost includes dollars, people, even organizational attention and reputation.

    Perhaps the validity of this triad is made more clear when one realizes that:

    SCOPE == “What you get”

    COST == “What you give”


    TIME is the dynamic variable linking the two.

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    I have no idea what the Unknown PM is talking about but I agree with most of your TC position especially about quality being part of scope. For example, in U.S. government development projects, the quality level is usually defined in the contractual specification.

    Certainly the triple constraints are alive and well as long as we have time and space in existence. The project TCs, of course, are time, cost and resources without any of which you cannot initate a project. Scope is what you accomplish using these limited constraints. Scope is usually envisioned as the area within a triangle where each side is a constraint. Change any side (constraint) of the triangle and the area within (scope) will change. What a simple and neat model!!!

    Risks are a resultant conditions of having to apply limited contraints to accomplish scope. So I don’t consider risks as constraints.

    Some may even argue that cost is really a resource and thus there are only two real project constraints, time and resources. Still, I like three triple contraints, it just feels right to me.

    Now for some levity. In her book, “Risk Management, Tricks of the Trade”, Rita Mulcahy defines the triple constraints as cost, time, scope, quality, risk and customer satisfaction. I guess the word triple has no real meaning to some “experts”.

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    Wow. From practical experience Alan I’d say
    people are way lucky just to hit the tripple
    constraints much less adding to them. As
    always your biggest challenge to even being
    allowed to successfully stick to your guns on the
    triple constraints will be your political skills
    dealing with upper management… this is of
    course the monstor hidden constraint of all
    projects which is never taught in any
    PM certification course.. how well do you manage
    up? So much for obsolecence of the triple
    constraints. Truth is you have to be pretty
    talented and lucky just to get those down ok in
    these environments. And as for those who say it’s
    inadequate well yeah of course and feel free to
    add more constraints, sounds great however that is
    sort of like someone living in a cardboard box
    saying a normal home isn’t adequate because they
    would like to live in a palace. Maybe starting
    with a normal home isn’t so bad if you live in the
    cardboard box of most projects. Now some
    methodologies need to rename everthing and call
    the obvious obsolete and that’s ok have your
    day in the sun I recognize that a rose is still
    a rose by any other name and they have just
    renamed those old obvious constraints. Look
    closely they are still there in highly iterative
    environments too, just shorter cycles where woops
    there they are again.

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