What is the underlying theory of project management?
„ Project Management Institute, 2002. Used with permission. In prior literature, it is generally seen that there is no explicit theory of project management (Shenhar 1998, Turner 1999). However, it is possible to find statements from the PMBOK Guide or the work of leading scholars on project management that approximate the definition of a theory or from which a theory can be deduced. Based on such core statements, we proceed in two steps. First, we crystallize the prescriptions (for action) and explicit principles of project management regarding a specific aspect or part of the project management process. Secondly, we compare this crystallization to the principles and prescriptions of candidate theories and identify a corresponding theory.
The PMBOK Guide states that projects are composed of two kinds of processes: project management processes and product-oriented processes (which specify and create the project product). Project management processes are further divided into initiating, planning, execution, controlling and closing processes. Let us first concentrate on the theory of the project proper (product-oriented processes), and then on the theory of management, covering the core processes of planning, execution and controlling.
Theory of project
In the following, we take the crystallization of Turner (1993) (also referenced in the PMBOK Guide) as a starting point for a reconstruction of the theory of project. According to Turner, scope management is the raison d’être of project management. He defines the purpose of scope management as follows: (1) an adequate or sufficient amount of work is done; (2) unnecessary work is not done; (3) the work that is done delivers the stated business purpose. The scope is defined through the work breakdown structure (WBS).
What does Turner say, from a theoretical point of view? Firstly, he (implicitly) claims that project management is about managing work; this is the conceptualization. Secondly, he claims that work can be managed by decomposing the total work effort into smaller chunks of work, which are called activities and tasks in the PMBOK Guide. Thirdly, he claims that this conceptualization and the principle of decomposition serve three essential purposes of project management. Even if not mentioned by Turner, there is an important, but implicit assumption associated with decomposition, namely that tasks are related if at all by sequential dependence.
Indeed, a review of the PMBOK Guide reveals that activities and tasks are the unit of analysis in the core processes of project management, like scope management, time management, and cost management, and that their management and control is centralized. This is also supported by the description of Morris of the classic - and still current - project management approach as follows (Morris 1994):
...first, what needs to be done; second, who is going to do what; third, when actions are to be
performed; fourth, how much is required to be spent in total, how much has been spent so far, and
how much has still to be spent. ... Central to this sequence is the Work Breakdown Structure
(WBS)...
When we compare this crystallization of project management to the theories of operations management in general, it is easy to recognize that it rests on the transformation theory (or view) of production, which has dominated production thinking throughout the 20th century. For example, Starr (1966) formulates:
Any production process can be viewed as an input-output system. In other words, there is a set of
resources which we call inputs. A transformation process operates on this set and releases it in a
modified form which we call outputs…..The management of the transformation process is what we
mean by production management.
In the transformation view, production is conceptualized as a transformation of inputs to outputs. There are a number of principles, by means of which production is managed (Koskela 2000). These principles suggest, for example, decomposing the total transformation hierarchically into smaller transformations, „ Project Management Institute, 2002. Used with permission. tasks, and minimizing the cost of each task independently. The transformation view has its intellectual origins in economics. The popular value chain theory, proposed by Porter (1985), is one approach embodying the transformation view. An explicit production theory based directly on the original view on production in economics has been proposed by a group of scholars led by Wortmann (1992). However, mostly the transformation view has been implicit – so embedded in thinking and practice that it has formed the basis of an invisible, unspoken paradigm that shapes behavior.

Theory of management
The PMBOK Guide divides project management processes into initiating, planning, execution, controlling and closing processes. Let us concentrate on the core processes of planning, execution and controlling (Exhibit 1). A central idea is that these processes form a closed loop: the planning processes provide a plan, that is realized by the executing processes, and variances from the baseline or requests for change lead to corrections in execution or changes in further plans.

Exhibit 1. The closed loop of managerial processes in project management according to the PMBOK Guide.
Theory of planning
The planning of projects is thoroughly described from the point of view of different knowledge areas in the PMBOK Guide. The planning processes are structured into core processes and facilitating processes. There are ten core processes: scope planning, scope definition, activity definition, resource planning, activity sequencing, activity duration estimating, cost estimating, schedule development, cost budgeting and project plan development. The output from these processes, the project plans, make up an input to the executing processes.
The planning processes dominate the scene in the PMBOK Guide: in addition to the ten planning processes, there is only one executing process and two controlling processes. The emphasis is on planning, with little offered on executing especially.
„ Project Management Institute, 2002. Used with permission. Comparison to theories in the general field of operations reveals that the perspective is that of management-as-planning (Johnston & Brennan 1996). Here, it is assumed that the organization consists of a management part and an effector part. Management at the operations level is seen to consist of the centralized creation, revision and implementation of plans. This approach to management views a strong causal connection between the actions of management and outcomes of the organization. By assuming that translating a plan into action is the simple process of issuing “orders”, it takes plan production to be essentially synonymous with action.

Theory of execution
How is the project plan executed? On this aspect, the PMBOK Guide is puzzlingly brief-worded. The only direct reference to the actual interface between plan and work is with regard to work authorization system, which is presented by four sentences:
A work authorization system is a formal procedure for sanctioning project work to ensure that work
is done at the right time and in the proper sequence. The primary mechanism is typically a written
authorization to begin work on a specific activity or work package. The design of the work
authorization system should balance the value of the control provided with the cost of that control.
For example, on many smaller projects, verbal authorizations will be adequate.
The underlying theory of execution turns out to be similar to the concept of job dispatching in manufacturing where it provides the interface between plan and work. This concept can be traced back to Emerson (1917). The basic issue in dispatching is allocating or assignment of tasks or jobs to machines or work crews, usually by a central authority. According to a modern definition, job dispatching is a procedure that uses logical decision rules to select a job for processing on a machine that has just come available (Bhaskaran & Pinedo 1991).
Obviously, dispatching consists of two elements: decision (for selecting task for a workstation from those predefined tasks that are ready for execution), and communicating the assignment (or authorization) to the workstation. However, in the case of project management, that decision is largely taken care in planning, and thus dispatching is reduced to mere communication: written or oral authorization or notification to start work. Here, the underlying theory seems to be the classical theory of communication (Shannon & Weaver 1949), where a set of symbols (voice or written speech) is transmitted from sender to receiver.

Theory of controlling
The PMBOK guide divides the core process of controlling into two sub-processes: performance reporting and overall change control. Based on the former, corrections are prescribed for the executing processes, and based on the latter, changes are prescribed for the planning processes.
Here we consider only performance reporting, based on performance baseline, and associated corrections to execution. They clearly correspond to the cybernetic model of management control (thermostat model) that consists of the following elements (Hofstede 1978):
. • There is a standard of performance
. • Performance is measured at the output (or input)
. • The possible variance between the standard and the measured value is used for correcting the process so that the standard can be reached.

This thermostat model is identical to the feedback control model as defined in modern control theory (Ogunnaike & Ray 1994).
„ Project Management Institute, 2002. Used with permission.

Discussion
Project management seems to be based on three theories of management: management–as planning, the dispatching model and the thermostat model. The first is evident from the structure and emphasis of the PMBOK Guide. The second is apparent from the discussion of execution in that Guide. The third is very clearly embodied in the closed loop of planning, execution and controlling as depicted in Exhibit 1. Neither theory comes as a surprise. Management-as-planning has been the widely held – even if most often implicit - view on intentional action in organizations up to now (Johnston & Brennan 1996). The dispatching model, closely associated with management-as-planning, has been common in industrial engineering from the beginning of the 20th century. Likewise, the thermostat model has been the dominating view on management in the 20th century (Giglioni & Bedeian 1974). These ideas were all current when project management emerged. Together they form the theoretical foundation of present management practice.