ANALYSIS: On the first day of Christmas my true love sent to me The One Minute Manager by Kenneth Blanchard and Spencer Johnson. I thought she might be trying to make a point.

On the second day of Christmas my true love sent me The Two Minute Motivator. A touch of desperation here, I thought.

On the third day, I was pleased to receive Michael Porter's three generic strategies - cost leadership, differentiation and focus. On the fourth day, my love presented me with the Boston Consulting Group matrix. There are four types of business in the firm's portfolio - cows, stars, dogs and question marks.

On the fifth day, back to Michael Porter again, for the five forces of buyers, competitors, suppliers, entrants and substitutes. On the sixth day, who better to turn to than Jack Welch for the six sigmas. And on the seventh day she drew my attention to Stephen Covey's Seven Habits of Highly Effective People.

And, like highly effective people, she stopped at seven.

Business literature and consultants' toolkits are full of lists. Most are between three and seven items long. Less than three is too few to have any weight. Covey would have done less well if he had written The Two Habits of Highly Effective People. But John Maxwell, author of 21 Indisputable Laws of Leadership and The 17 Essential Qualities of a Team Player, erred in the other direction.

Seven is the longest list most people can manage - seven deadly sins, seven seas, seven wonders of the world, seven ages of man and the seven colours in the rainbow.

We recognise seven notes in the western musical scale. The seven colours and seven notes are not found in the natural environment. They are products of the way we see the environment.

Our instinct is to construct lists and impose categories, even where there are no natural categories. And the lists we use are typically between three and seven items long. Neurophysiologists are beginning to understand why.

We possess a "working memory" rather like the desktop on a computer, which contains matters you are dealing with right now. Its capacity is generally three to seven categories.

The job of the business guru is to find lists of between three and seven items that enable clients to categorise a complex world in an ordered way.

That doesn't mean any old categorisation will do. I once spent a session with company managers who were debating how they should apply concepts presented by their expensive consultants. Was the company a hunter or a gatherer? Were its customers empty-nesters or surfers?

They couldn't do it because the consultants' categories simply did not match the way the managers saw their business.

Categorisation is rough and ready. In Britain, blood and a pillar box are described as red, although their colours are different. The similarity seems more important than the difference.

So are our categories innate or the product of culture and environment? Some anthropologists tested this issue by showing paint swatches to primitive tribes with simple languages. They discovered that almost every language distinguished white, black and red.

The fourth and fifth colour words were always either green or yellow. If a language had as many as six colour words, it had a word for blue. And if it had seven colour words, there was a word for brown.

Although there are very many ways in which colours could be categorised, the ways in which humans do it are more or less independent of their culture or language. There are some kinds of description that somehow feel right to us, while others don't.

Seven colour words seem to be enough. You can describe anything you can see with seven colours.

English, with far more words than other languages, has concepts such as amber and magnolia, which are muddy hybrids of existing colours.

You can have too many categories to guide your choices, as you find when you go to a paint shop in search of green and the salesman asks whether you were looking for pistachio or spring grass.

Or too few: it is, of course, restrictive to have to describe either the physical world or the business world in terms of black and white. - (Financial Times Service)