The psychologist Abraham Maslow's theory of human motivation is 70 years old but continues to have a strong influence on the world of business. What is it, and is it right?
There is a commonly reproduced symbol which many believe holds the secret to personal fulfilment and business success.
It usually takes the form of a triangle, but variants in the shape of 3D pyramids and staircases are not uncommon. It regularly appears in university psychology modules, and may pop up in other degree courses too. On management training courses it's as inevitable as biscuits and role-playing.
In 1943, the US psychologist Abraham Maslow published a paper called A Theory of Human Motivation, in which he said that people had five sets of needs, which come in a particular order. As each level of needs is satisfied, the desire to fulfil the next set kicks in.
First, we have the basic needs for bodily functioning - fulfilled by eating, drinking and going to the toilet. Maslow also included sexual needs in this group.
Then there is the desire to be safe, and secure in the knowledge that those basic needs will be fulfilled in the future too. After that comes our need for love, friendship and company. At this stage, Maslow writes, the individual "may even forget that once, when he was hungry, he sneered at love".
The next stage is all about social recognition, status and respect. And the final stage, represented in the graphic as the topmost tip of the triangle, Maslow labelled with the psychologists' term "self-actualisation".
It's about fulfilment - doing the thing that you were put on the planet to do. "A musician must make music, an artist must paint, a poet must write, if he is to be ultimately happy," wrote Maslow. "What a man can be, he must be."
While there were no pyramids or triangles in the original paper, Maslow's hierarchy of needs is now usually illustrated with the symbol. And although the paper was written as pure psychology it has found its main application in management theory.
"There's no question it's had a profound influence on management education and management practice," says Gerard Hodgkinson, a psychologist at Warwick Business School. "One of the insights is that as managers we can shape the conditions that create people's aspirations."
Managers use Maslow's hierarchy to identify the needs of their staff and help them feel fulfilled, whether it's by giving them a pet project, a fancy job title or flexible working arrangements, so they can pursue their interests outside the workplace.
In the second half of the 20th Century, bosses began to realise that employees' hopes, feelings and needs had an impact on performance. In 1960, Douglas McGregor published The Human Side of Enterprise, which contrasted traditional managerial styles with a people-centred approach inspired by Maslow. It became a best-seller.
Some managers began to move away from a purely "transactional" contract with a company's staff, in which they received money in exchange for doing a job, to a complex "relational" one, where a company offered opportunities for an individual to feel fulfilled, but expected more in return.
Bill O'Brien, President and CEO of Hanover Insurance, put it well in an interview published in 1990. "Our traditional organisations are designed to provide for the first three of Maslow's hierarchy of human needs," he said. "Since these are now widely available to members of industrial society our organisations do not provide significantly unique opportunities to command the loyalty and commitment of our people."
According to Douglas Kenrick at Arizona State University, the appeal of Maslow's hierarchy can be explained by the fact that it reflects a pattern of growth we observe in children.
"I have a child who is six years old and I noticed that when he was an infant he couldn't care less about public opinion," Kenrick says. "In kindergarten he started to worry about making friends but he didn't really care about getting respect from those people. And now he's in the first grade and you can see he's beginning to think about his friends' opinions and what status they hold him in."
Kenrick also thinks the longevity of the hierarchy of needs can be explained by the pyramid which came to represent it, and which "captures a complicated idea in a very simple way". Maslow's theories have many supporters today, including US hotelier and business guru Chip Conley.
But critics point to dozens of counter-examples. What about the famished poet? Or the person who withdraws from society to become a hermit? Or the mountaineer who disregards safety in his determination to reach the summit?
Muddying things slightly, Maslow said that for some people, needs may appear in a different order or be absent altogether. Moreover, people felt a mix of needs from different levels at any one time, but they varied in degree.
There is a further problem with Maslow's work. Margie Lachman, a psychologist who works in the same office as Maslow at his old university, Brandeis in Massachusetts, admits that her predecessor offered no empirical evidence for his theory. "He wanted to have the grand theory, the grand ideas - and he wanted someone else to put it to the hardcore scientific test," she says. "It never quite materialised."
However, after Maslow's death in 1970, researchers did undertake a more detailed investigation, with attitude-based surveys and field studies testing out the Hierarchy of Needs.
"When you analyse them, the five needs just don't drop out," says Hodgkinson. "The actual structure of motivation doesn't fit the theory. And that led to a lot of discussion and debate, and new theories evolved as a consequence."
In 1972, Clayton Alderfer whittled Maslow's five groups of needs down to three, labelled Existence, Relatedness and Growth. Although elements of a hierarchy remain, "ERG theory" held that human beings need to be satisfied in all three areas - if that's not possible then their energies are redoubled in a lower category. So for example, if it is impossible to get a promotion, an employee might talk more to colleagues and get more out of the social side of work.
More sophisticated theories followed. Maslow's triangle was chopped up, flipped on its head and pulled apart into flow diagrams. Hodgkinson says that one business textbook has just been published which doesn't mention Maslow, and there is a campaign afoot to have him removed from the next editions of others.
The absence of solid evidence has tarnished Maslow's status within psychology too. But as a result, Lachman says, people miss seeing that he was responsible for a major shift of focus within the discipline.
"He really was ground-breaking in his thinking," Lachman says. "He was saying that you weren't acting on the basis of these uncontrollable, unconscious desires. Your behaviour was not just influenced by external rewards and reinforcement, but there were these internal needs and motivations."
Unlike the psychoanalysts and behaviourists who preceded him, Maslow was not that interested in mental illness - instead of finding out what went wrong with people, he wanted to find out what could go right with them. This opened the door for later movements such as humanistic psychology and positive psychology, and the "happiness agenda" that preoccupies the current UK government.
Maslow's friend, management guru Warren Bennis, believes the quality underlying all Maslow's thinking was his striking optimism about human nature and society.
"Abe Maslow, a Jewish kid who really grew up poor, represented the American dream," he says. "All of his psychology really had to do with possibility, not restraints. His metaphysics were all about the possibilities of change, the possibilities of the human being to really fit into the democratic mode."
Photos of Maslow courtesy of the Robert D. Farber University Archives & Special Collections, Brandeis University.
Health Check is broadcast on the BBC World Service. You can listen to the episode about Abraham Maslow on iPlayer.