The Complementary Management Model

Abstract

This chapter introduces a new theoretical model of people management and leadership. The Complementary Management Model describes it as a bundle of specific tasks that represent preconditions of human performance. The two service functions of support and discipline are concretized in each of the tasks. Ideally, the employee fulfills all of these tasks in their entirety as a self-manager. As a complementary actor, the line manager intervenes in a compensatory manner only when the employee is unable to fulfill these management tasks. If this does not happen, senior managers and HR advisors step in. Through these three elements of the core model, Complementary Management ties in with, among other things, the theoretical approaches of Shared Leadership and Leadership as a Service as well as with task models of leadership and management. Implementing this core model requires four further elements: management routines, management instruments, management unit design, and management resources. The systematic relationship can be summarized as follows: the management actors fulfill management tasks (e.g., performance feedback) using management routines (e.g., interviews), apply management instruments (e.g., work schedules), require management resources (e.g., business information), and do all this on the basis of the unit structures (e.g., the design of their job). The main purpose of the model is to provide a theoretical basis for corporate models (= principles and guidelines) of management and leadership.

Full text

* This text is an excerpt of the book “Complementary Management: A Practice-
driven Model of People Management and Leadership in Organizations” by Boris
Kaehler (Springer 2022). Reproduced with the kind permission of the publisher.
Complementary
Management
A Short Overview*

2Complementary Management - A Short Overview
The Theoretical Modelʼs Subject and
Aspirations (▶ Section 2.1)
a ) Subject Matter, Purpose and Development Stage
The subject of the Complementary Management (or Complementary Leader-
ship) Model is people management and leadership in organizations1. The term
Complementary Management is derived from the three elements of the core
model, each of which has complementary components. For instance, the two
complementary management functions – the support function and the disci-
plinary function – make up the totality of the management service. The range
of complementary management tasks together generates the totality of the
human performance conditions, which consist of enabling and carrying out
work in order to achieve organizational goals. And nally, the complementa-
ry management actors together make up the totality of the key participants
whose joint action shapes the management process.
In its current form, the Complementary Management Model is the result of a
theoretical conceptualization process that has developed over many years. It
started out as a broad outline and was subsequently further developed, with
publications to date reecting the respective stage of development (see Kaeh-
ler 2012, 2013, 2014a, b, 2017, 2020). Like most forms of systematic theorizing,
it is based on practical observations, literature studies, and conceptual ideas
that are condensed into a consistent web of theoretical assumptions (see, e.g.,
Neuberger 2002, p. 393 ff.). The individual mechanisms have been tested in
practice and reect functional people management and leadership as it is
practiced in many organizations. The overall model has been applied in vari-
ous companies and substantially rened on the basis of the experience gained.
Next, empirical studies should be carried out which accompany its implemen-
tation in organizations and examine its effectiveness.
b ) Objective and Benet
Anyone seeking to understand and shape leadership and management in or-
ganizations needs a theoretical framework. The intention of Complementary
1 For theoretical reasons explained in ▶ Section 1.2, management and leadership are
used synonymously here. Since this will inevitably collide with the common unders-
tanding of many readers, I sometimes use “management and leadership” to facilitate
reading.

3
Complementary Management - A Short Overview
Management Theory is to illustrate how people management and leadership
are to be designed in order to best achieve their purpose of fullling the goals
of the organizational unit by generating work performance and meeting other
requirements. The theory is descriptive in the sense that it describes mecha-
nisms of people management and leadership that are actually used and which
function in practice. At the same time, it is normative in the sense that it clear-
ly recommends that – with certain adaptations – leadership and management
in organizations should precisely follow this pattern. By no means does the
theoretical model need to depict and explain all of the conceivable aspects of
leadership and management - only those that can be meaningfully generalized
and standardized.
Even though the Complementary Management Model is also intended to be of
scientic use and to serve as an orientation for managers, its main purpose is
to provide a theoretical basis for corporate models (= principles, guidelines) of
management and leadership. These are fundamental stipulations relating to
leadership and management in a specic organization in the sense of a consti-
tution of personnel work. They dene why, by whom and how a specic orga-
nization or organizational unit (including its personnel) is to be managed and
led. Organizations designing such corporate models may use some or all ele-
ments of Complementary Management and should progress with the project
in ve phases (see ▶ Section 2.6).

4Complementary Management - A Short Overview
Initial Conceptional Considerations (▶ Chapter 1)
a ) Underlying Concept of Management and Leadership
Organizational management, in the sense of managing people, is an inuence
on people in an organization and its units with the aim of achieving the unit’s
objectives by generating work performance and meeting other requirements.
To lead a unit or its members is synonymous with “directing” or “leading”
them. The deliverables of people management and leadership consist rstly of
the short- and long-term work performance of employees, secondly of short-
and long-term personnel costs, and thirdly of the fulllment of other require-
ments made by the market, the legal situation, and the stakeholders.
Management and leadership inuence can be exercised in two ways: through
anticipatory norm-setting or through situational intervention. Both forms can
be exercised in hard, externally directed ways or in gentle, non-directive ways.
Since hard external inuence usually triggers resistance, it is advisable to pri-
marily exert inuence in a gentle manner (e.g., in the form of systematic self-
direction, instrumental behavioral reinforcement, nudging, collective social
norms, or implicit communication).
Management and leadership in organizations, which are highly structured
contexts, must be distinguished from political leadership, i.e., being a leader
in poorly structured contexts, even though many sources narrow it down to
just that. However, people management/leadership, employee management/
leadership, and human resource management/leadership are one and the
same. Of course, certain aspects of management and leadership are usually
assigned to the HR department and others to line managers/leaders. However,
these are not separate spheres but rather a division of labor in dealing with a
single mandate, namely leadership and management of personnel.
b ) Balance of Regulations and Latitudes
Normative recommendations for leadership are only effective if they contain
a meaningful balance of regulations and regulation-free spaces. If corporate
people management and leadership is to work well across the whole company,
structures and responsibilities must be dened. At the same time, degrees of
individual and situational freedom are needed in the right places. Organizati-
ons have room for discretion here. Even though certain aspects of leadership
– including functions, tasks and actors – need to be regulated, others – e.g.,
situational and individual modes of application – most denitely should not
be. Whether formal leadership rules are actually transformed into informal

5
Complementary Management - A Short Overview
structures and everyday behavior depends on whether they are a) functional,
and b) consistently communicated and called for.
c ) Complexity of Theoretical Management Models
Whether or not Complementary Management is a theory or a theoretical
model depends on one’s notion of the term and comes down to quibbleism. In
fact, most social and economic science theories are limited to simple causality
relations between a few variables. The Complementary Management Model
is composed of seven model elements, each with various partial elements as
well as interrelations, and is therefore quite complex. Those who consider this
to be too overblown may prefer to visualize the theoretical complexity of ma-
king coffee or driving a car: How many elements could these be broken down
into? The expectation of dealing with a useful theoretical or practical leader-
ship model in a few sentences and making it comprehensible at rst glance is
just as unrealistic as explaining how to drive a car in a few short steps. The lack
of practical relevance for many scientic studies may be nothing more than an
indicator for the incompleteness of the underlying theories.
Fig. 1.3The role of HR in the three elds of management activity (modied from Kaehler and
Grundei 2019, S. 33; © Boris Kaehler/Jens Grundei. All rights reserved.)
Corporate Management
(= Management)
Operations
(= Execution)
Market
Operations
Operative Management
Direction of day-to-day operations by managing people
Strategic Management
Determination of strategies for a certain time period
incl. HR strategies
Marketing
Sales/Distribution incl. Logistics
Fabrication or Service incl. Logistics
Research and Development
Financing/Investments/Accounting
Information/Data Operations
Material Purchase/Storage/Disposal incl. Logistics
Production
Operations
Resource
Operations
Constitutive Management
Determination of permanent internal norms
incl. business model, stakeholder denition etc.
incl. org. unit and process design, culture, code of conduct
incl. internal factual-technical and HR governance

6Complementary Management - A Short Overview
d ) People Management and Leadership as a Part of Corporate
Management
Organizational people management and leadership is a part of organizational
management in the sense of managing an organization. This is dened as a
steering inuence on market, production and/or resource operations in an or-
ganization and its units that may address both people and non-people issues
with the aim of achieving the unit’s objectives. This theoretical differentiation
between steering and execution only makes sense, of course, if the steering
also exists as self-steering, which it indeed does. It can be subdivided into three
areas: constitutive management is about the basic set-up and positioning of
the unit, strategic management is about steering the business within a certain
timeframe, and operational management is about the ongoing implementa-
tion of the strategic guidelines. All three task elds are required at the overall
organization level, but also at the level of each organizational unit. Against
this backdrop, the prominent role and relevance of people management and
leadership for success becomes clear: It is indeed a specic form of resource
administration (“human resource management”), and as such is on par with,
for example, the company’s administration of nancial or material resources.
At the same time, however, it encompasses all operational management, since
all activities in all areas of the business are carried out by people who are to be
managed, i.e., led.

7
Complementary Management - A Short Overview
The Three Elements of the Core
Model (▶ Chapter 2)
The core model of Complementary Leadership contains the fundamental
aspects and mechanisms of people management and leadership in organizati-
ons. It describes them as a bundle of 24 tasks in which two functions take form
and which are accomplished by ve main actors (see Figure 2.1).
1. Complementary Management Functions: Leadership as a Service
The rst element of the core model consists of the complementary manage-
ment functions. Organizational people management and leadership are un-
derstood to be an internal service. This service has two functions with respect
to the personnel in an organizational unit. The support function is to help in-
dividual employees perform their jobs. The catchwords „to foster“, „apprecia-
tion“ and „employee orientation“ illustrate this. The disciplinary function is
to discipline and supervise the performance of individual employees. The cat-
chwords here are „to demand“, “added value” and „production orientation“.
In terms of management and leadership theory, the model element thereby
ties in with the approach of „management as a service“ and the classic duality
Fig. 2.1Core Complementary Management
Model with a sample distribution of actors per
task category (modied from Kaehler 2014b, p.
460; © Boris Kaehler 2019. All rights reserved.)
Line manager
Colleague
Employee
Senior Manager
HR Manager
Creating
Motivation
Hiring,
retaining,
separating
Ensuring
administration
Granting
Care
Fostering
competence and
development
Arranging
Collaboration
Managing
work tasks
S
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p
p
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t
F
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D
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F
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Setting
HR norms

8Complementary Management - A Short Overview
of „employee orientation” vs. “production orientation”. It has the status of a
fundamental principle and is primarily of practical value: The idea of manage-
ment as a dual service provides orientation for leaders and prevents destruc-
tive leadership.
2. Complementary Management Tasks:
Leadership as a Bundle of Tasks
The complementary management tasks form the second model element. Peo-
ple management and leadership consists of 24 tasks that can be grouped into
eight categories: “Setting HR norms,” “Hiring, retaining, separating,” “En-
suring administration,” “Managing work tasks,” “Arranging collaboration,”
“Fostering competence and development,” “Granting care,” and “Crafting
motivation”. This is based on the premise that precisely these inuences are
required to generate sustainable human performance. The model is thus in
the theoretical tradition of normative task models of leadership and manage-
ment. However, the management tasks are not understood as activities, but as
abstract goals to be realized within the framework of concrete activities („ma-
nagement routines“). All 24 tasks together complement each other to form the
overall task of people management and leadership. In each task, both the disci-
plinary and the support function are specied.
Task
Category
Task Task Content in Detail
Setting
HR norms
To stipulate HR
governance/HR
strategies
• The operational leadership and management of the em-
ployee follows a coherent and functional internal HR
governance consisting of the corporate management
model as a metastructure and the HR infrastructure as a
set of detailed regulations pertaining to structure, inst-
ruments, routines and resources.
• It also follows a coherent and functional HR strategy;
all operational areas of HR management (= the other 21
leadership/management tasks) are backed up in this
strategy by strategic goals and demand scenarios for the
coming business period.
To optimize orga-
nizational design/
processes
• All work processes as well as the job and hierarchical
integration of each employee are optimized in terms of
time, cost and quality.
• These processes and structures are documented in a
comprehensible manner.
To shape culture
and diversity
• Clear cultural standards - shared values and appearan-
ces - applicable to the employee are set at the level of
each organizational unit to which he or she belongs.
• Clear diversity standards - welcomed differences and
rules to protect them - applicable to the employee
are set.
• General rules of conduct (conduct, handling conicts
of interest, etc.) applicable to the employee are clearly
dened.

9
Complementary Management - A Short Overview
Hiring,
retaining,
separating
To recruit
and retain
• Applicant target groups with a high prole t are
dened.
• All four sourcing areas (external and internal labor mar-
ket, peripheral or pseudo workforces, and internal e-
xibility reserves) are considered with the dened target
groups in mind.
• Appropriate candidates are recruited.
• Applicant relationships are systematically maintained.
• Top performers are retained.
To select and
put onboard
• The requirement proles of the positions are accurately
recognized.
• Personnel selection is carried out in an “end-to-end”,
process-oriented manner and by means of planned ap-
titude testing.
• Jobs are lled exclusively with suitable and highly ca-
pable candidates.
• New employees are systematically integrated.
To dismiss
and release
• Possible miscasts are dismissed.
• Possible surplus personnel are reduced.
• Organizational arrangements are made in the event of
unwanted attrition.
Ensuring ad-
ministration
To handle HR ad-
ministration
• The administrative work related to the employee is
taken care of.
To collect and ana-
lyze data
• The data relevant to the employee and his or her work
are collected and evaluated in order to identify optimi-
zation potentials.
To look after
employee repre-
sentatives
• Functional relationships exist with works councils as
well as trade unions and other bodies representing staff.
Managing
work tasks
To dene work
tasks and inst-
ructions
• The work tasks and work specications of the employee
are sensibly dened and known to him or her.
• Development-oriented work task management is prac-
ticed, from small-scale leading with instructions to lea-
ding with objectives and self-control.
To provide wor-
king time and
resources
• The employee is provided with working time, material
resources and a nancial budget in accordance with the
tasks at hand.
To evaluate per-
formance and give
feedback
• The work performance of employees is comprehensively
appraised, and he or she knows how to properly judge it.
Arranging col-
laboration
To ensure coor-
dinative com-
munication
• The employee is continuously informed about the issu-
es that are relevant to him or her.
• The technical and functional need for coordination with
the other group members is determined and the coordi-
native communication is conducted accordingly.
• Wrong decisions and loss of creativity in groups are sys-
tematically prevented.
To maintain re-
lations and solve
conicts
• The employee assumes responsibility for relationships
in all directions and maintains internal and external
networks.
• There is a constructive conict culture.
• Manifest conicts are resolved quickly.
To enhance group
cohesiveness and
identication
• There is an appropriately strong group cohesion.
• The team members identify with the collective.

10 Complementary Management - A Short Overview
Fostering
compe-
tence and
development
To qualify • Qualification gaps of the employee are identified
and closed.
To develop
• The employee‘s development potential is identied and
systematically implemented.
• Alternatives to a management career are also identied.
To cultivate
knowledge and
innovation
• Existing knowledge of the employee is tapped and sha-
red with others as needed.
• Divergent and convergent thinking achieves continuous
improvement and innovation.
Granting care
To protect health
and life balance
• Health hazards are minimized, and disaster, pandemic
and threat scenarios are in place.
• The health and work-life balance of the employee are
protected, and permanent work overload is prevented.
• Resilience and the ability to cope with balance crises are
strengthened.
To create ow
conditions
• The employee has a sense of control with respect to his
or her work and its conditions.
• Work design enables and promotes the phenomenon
of ow.
To explain and ac-
company change
• The employee understands the necessity and the con-
text of upcoming changes.
• Individual adaptation needs and requirements in con-
nection with changes are taken into account.
Crafting
motivation
To consider needs
and wants
• The permanent motive structures of the employee are
recognized and taken into account.
• The current motives of the employee are recognized and
taken into account.
To round off the in-
centive eld
• The real existing eld of inducements of the managed
person is continuously analyzed.
• Additional activity inducements, option inducements,
social inducements and monetary inducements are set
in order to compensate for misaligned incentives and to
generate additional motivation.
To inuence
expectations/
goals/impulse
• Performance, change, incentives and justice expectati-
ons are consciously shaped.
• The work activity is experienced as meaningful.
• Goals and behavioral intentions correspond to work re-
quirements.
• The employee feels the necessary behavioral impulses
to actually take action.
Tab. 2.5The tasks of people management and leadership in organizations (modied from Kaeh-
ler 2014a, p.82, 2017, p. 174; © Boris Kaehler 2019. All rights reserved.)

11
Complementary Management - A Short Overview
3. Complementary Management Actors:
Leadership as Shared Leadership
The third element of the core model encompasses the complementary ma-
nagement actors. People management and leadership is the responsibility of
several key players: the employee, his or her colleagues, the line manager, the
senior manager and the HR advisor. The primary management principle should
be self-management, i.e., the employee should ideally take on all leadership/
management tasks him or herself. Since not all employees always do this, the
line-manager must intervene in a compensatory manner when necessary. If he
or she does not, it is up to the senior manager and the HR advisor acting as „co-
HR manager“ to intervene in a compensatory manner. These interventions can
be corrective, joint, delegative or substitutive. The complementary actors thus
complement each other and collectively perform the 24 management tasks.
This compensatory mechanism ensures, on the one hand, that all manage-
ment tasks are actually performed with regard to each individual employee
even if the line manager is inactive, thus ensuring that work is performed. On
the other hand, this multi-entity system is suitable for preventing an abuse
Fig. 2.2Compensatory-situational interaction of the management actors (modied from Kaehler
2014b, p. 460; © Boris Kaehler 2019. All rights reserved.)
Employee
Colleague
Manager
Senior Manager
HR Manager
Example 1:
Manager and colleagues compensate
for self-leadership deficits of employee
Example 2:
Senior manager and HR manager compensate
for leadership deficits of manager
Gap
Gap

12 Complementary Management - A Short Overview
of power by the line manager. In terms of management and leadership theo-
ry, the element of complementary management actors takes up the „Shared
Leadership“ approach, which is combined with the concept of self-manage-
ment and with a vertical-hierarchical exercise of authority based on the prin-
ciple of exception.
The core model of Complementary Management thus describes people ma-
nagement and leadership as a bundle of 24 tasks in which two service functi-
ons incorporate themselves and which are accomplished by ve main actors.
With these three core elements, it forms a counter-concept, so to speak, to the
widespread idea of leadership as a personality-based or systemic relationship
phenomenon (= in which there is a lack of clearly dened leadership/manage-
ment tasks) brought about by line managers (= in which there is a lack of other
actors) which confers on them a reign-like self-image (= in which the idea of
service is lacking).

13
Complementary Management - A Short Overview
The Four Implementation
Elements (▶ Section 2.5)
Implementing it requires four further model implementation elements: ma-
nagement unit design, management routines, management instruments and
management resources. The systematic relationship can be summarized as
follows: Managers full management tasks (e.g., performance feedback) using
management routines (e.g., interviews), apply management instruments
(e.g., work schedules), require management resources (e.g., business informa-
tion), and do all this on the basis of the management unit structure (e.g., the
design of their job).
4. Management Routines
The management routines, understood as concrete activities, serve as a way
to implement the management tasks. For example, performance feedback is
initially only an abstract task that must be implemented in regular employee
dialogs, among other things. A distinction must be made between annual rou-
Fig. 2.3Core model and
implementation elements
of Complementary Manage-
ment (modied from Kaehler
2017, p. 317; © Boris Kaehler
2019. All rights reserved.)
M
a
n
a
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e
m
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n
t
U
n
i
t
s
Creating
Motivation
Ensuring
administration
Hiring,
retaining,
separating
Granting
Care
Fostering
competence and
development
Arranging
Collaboration
Managing
work tasks
S
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p
p
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t
F
u
n
c
t
i
o
n
D
i
s
c
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p
l
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n
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F
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n
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t
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o
n
Setting
HR norms
Management
Routines
M
a
n
a
g
e
m
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n
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s
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f
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m
a
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i
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W
o
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k
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T
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a
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a
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e
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t
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o
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M
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F
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b
a
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k
Implementation Elements
(Routines, Instruments, Resources, Units)
Core Model
(Functions, Tasks, Actors)

14 Complementary Management - A Short Overview
tines (e.g., annual employee reviews), continuous routines (e.g., weekly work
dialogs) and on-demand routines (e.g., crisis interventions or hiring projects).
The theoretical basis of this element of the management model is the esta-
blished construct of organizational routines. Those for whom the term has a
negative connotation (in the sense of getting stuck in a rut) may replace it with
“management activities”. Organizations should clearly dene which manage-
ment routines are to be performed, which actors are involved, and what the
frameworks are. The shares each actor has in the routines add up to the totality
of their people management activities. This puts management responsibilities
into very concrete terms: Has an actor actually carried out the routines incum-
bent upon him or her and thereby achieved the dened management tasks? If,
for example, a line manager does not conduct regular work dialogs, he or she is
simply neglecting his or her professional duties.
5. Management Instruments
Within the framework of management routines, management actors use the
management instruments available in their respective companies. These are
formalized tools that support employee management and leadership, in par-
ticular, rules, systems, programs and forms. The conceptual differentiation
between routines and instruments has signicant implications. Leadership
and management are not exercised through the instrument (e.g., a salary sys-
tem or appraisal procedure), but always through its specic application. Good
instruments are sometimes devalued by their inadequate use in everyday ma-
nagement. Conversely, dysfunctional and poorly designed HR instruments can
be relativized in the course of their application and misguided decisions can
be avoided - a question of management quality and certainly also a question
of the internal distribution of roles. Above all, however, it becomes clear that
HR instruments must be designed in such a way that they effectively support
day-to-day people management and leadership.
6. Management Unit Design
The management unit design encompasses the organizational structures in
which the various management actors are integrated. This relates to the struc-
ture and hierarchical integration of the organizational units involved in people
management and leadership (jobs, groups, departments, divisions, etc.). Ho-
wever, the distribution of tasks among the actors and their respective powers
are also connected with it. The general principles of organizational science
form the theoretical basis here. The management unit design, like the other
elements of the model, does not represent a sub-area of leadership, but pro-
vides a special perspective on leadership and management. Thus, it cannot be
considered separately from the overall model. Inuencing processes certainly

15
Complementary Management - A Short Overview
take place without permanent management structures, but this has little to
do with systematic organizational leadership and management. The Comple-
mentary Management Model leaves room for different distributions of tasks
among the actors, but its elements provide a rough structural framework. For
example, a human resources department that refuses to accept compensatory
„HR co-management“ would not be compatible with the model. The same ap-
plies to management positions without disciplinary authority or with an over-
stretched management span. Functioning people management and leadership
requires a functional management unit design.
7. Management Resources
In the Complementary Management Model, the implementation element of
management resources represents a purely pragmatically reasoned selection
of management prerequisites critical to success. In practice, leadership and
management often fail because of four essential problematic resources - so
much so that it is worth highlighting them prominently by means of a separa-
te element. First: the working time required to perform management routines,
which many leaders do not have or do not take. Second, management compe-
tencies are required. These consist of action competencies (i.e., skills to suc-
cessfully perform management routines), which in turn are based on non-ma-
nagerial elemental competencies (e.g., communication, analysis, assessment,
decision-making). Third, management actors need comprehensive directional
and situational information. And nally, holistic management feedback is
required. All four resources are necessary to enable effective people manage-
ment and leadership in the rst place.

16 Complementary Management - A Short Overview
Literature
Kaehler, Boris (2012): Komplementäre Führung – Ein Beitrag zur Theorie und
konzeptionellen Praxis der organisationalen Führung; epubli Verlag/Holtz-
brinck 2012.
Kaehler, Boris (2013): Aufgabenorientierte und komplementäre Führung –
Grundzüge eines integrativen Modells (Boris Kaehler); Personalführung Juli
2013, pp.30–37.
Kaehler, Boris (2014a): Komplementäre Führung – Ein praxiserprobtes Modell
der organisationalen Führung; 1st edition Springer Gabler 2014.
Kaehler, Boris (2014b): Komplementäre Führung – Ein neues Führungsmodell;
Arbeit und Arbeitsrecht 8/2014 (Jahrgang 68); pp.459–461.
Kaehler, Boris (2017): Komplementäre Führung – Ein praxiserprobtes Modell
der Personalführung in Organisationen; 2nd edition Springer Gabler 2017.
Kaehler, Boris (2019): Führen als Beruf; 1st edition Tredition 2019.
Kaehler, Boris (2020): Komplementäre Führung – Ein praxiserprobtes Modell
der Personalführung in Organisationen; 3rd edition Springer Gabler 2020.
Kaehler, Boris (2022): www.complementarymanagement.com (Accessed
01/05, 2022)