Collections are back in fashion. After a couple of decades during which there were some within museums, and many without, who wondered whether experiences and interactives might not communicate better than stubbornly static and sometimes enigmatic objects, there has been a rediscovery of the value of encountering the thing itself.

A realisation perhaps that objects can change their meaning according to the mood and needs of the viewer, altering their impact through time in a way that pure interpretation never can: there is nothing more dated than yesterday's interactive.

Certainly Estelle Morris's Understanding the Future: Museums and 21st-Century Life regards it as self evident that 'collections are at the heart of all that museums do'. And now the Museums Association's Collections for the Future report proclaims that 'collections are central to everything that museums do and all that they might achieve'. Amen to that.

But there is still, in both documents, a sense of unease about collections and their use; a sense that we need to find new ways of understanding their purpose and future. To understand the source of this unease we have to understand that there is a gap between the stories that museums tell about themselves, and the reality of their evolution and the real experience that they provide.

The British Museum's story was about the pursuit of knowledge, the National Gallery talked of art for the people, the Victoria and Albert Museum (V&A) intended to help train designers and educate public taste. From the beginning, museums have been embedded in a utilitarian culture. They want to be used and useful, diverse and democratic.

But look at their collections. Museums often talk as though they were dedicated documenters of history through material culture, but actually they have always tended to ignore the representative in favour of the exceptional, the useful in favour of the useless, the commonplace in favour of the rare.

Science museums prefer prototypes to production models, social history museums collect vanishing, rather than typical, lifestyles, ethnographers prefer exotic and marginal to dominant cultures. People often say that the V&A is full of objects that were used in everyday life.

The opposite is true. Of the beds in the British Galleries, one was made way over life-size to advertise an inn, another was a bed of state made to affirm status, not to promote sleep. The hierarchy of status within which we all work has at its pinnacle fine art, which is of course defined precisely by its lack of the demeaning function that would condemn it as 'applied'.

If we could be more honest about the motives that bring collections into being, and result in their acquisition by museums, we could perhaps be more clear thinking about their future. Collecting is, and has always been, closely connected with the acquisition and retention of status. It is competitive. My stamp is rarer than your stamp. Children say these things out loud. The way that paint is handled in my Monet is more fluent and fluid than in your Pissarro.

Adults can hide competition under a camouflage of connoisseurship. American cities vie with one another to have the most spectacular art museums with the most 'important' collections. Rather a giveaway word, 'important'. I have never heard a museum director or trustee describe their collection as exceptionally useful, but we are regularly told that a collection is very important, or internationally significant.

There is nothing shameful about this. If you are glad, as I am, that the National Gallery has a fine collection of Raphaels, we need to feel free to admit that it is OK to be pleased about this, not only because such beautiful images are a source of lasting pleasure, but also because our community has been able to acquire such wonderful things for public enjoyment.

Museums are full of gifts. Elaborate, costly and beautiful things that were made to please the recipient and enhance the status of the giver. And they are full of collections of costly and beautiful things that were then given to the museum and so to the community as a whole.

Given the questions of status and pride involved, it is no wonder that the older buildings they inhabit are colonnaded, high-ceilinged, and elevated above the crowd, or that contemporary museums vaunt their magnificently wasteful atria and halls; no wonder that, whether 19th, 20th or 21st century, they speak of grandeur and conspicuous consumption.

A donor of my acquaintance surprised me when discussing giving to museums by asserting, 'It's potlatch'. His reference was to the traditional west coast American-Indian practice of spectacularly destroying prestige goods in a ceremony that confers status on the destroyer.

What he meant, I think, was that in many, if not all, societies, status is established by the possession of things that are rare and difficult to come by. But museums are about preservation, not destruction. A closer analogy than potlatch might be ritual deposition. In medieval and early modern Europe, objects of the highest status were, it could be argued, ritually deposited in cathedrals and monasteries.

The gift of precious objects by the rich and powerful to the god of the poor, not only sanctified and legitimised the possession of wealth by putting it to a charitable purpose, but also locked up such objects in a sacred place where they could be seen and admired, but no longer given or traded.

In more recent times museums have fulfilled a similar role. The generosity of those who give their treasured collections to the public also ensures that these objects are taken out of the market and remain forever associated with their last private owner.

No wonder then that there is anxiety around museum collections, and particularly around disposal: few things are more hurtful than the neglect or rejection of a gift. But recognising and working with this reality, we can continue to assert that museums do also have great utility: that their ability to serve the public interest is enhanced, not hindered, by the fact that they serve a variety of purposes, both instinctual and rational.

Collections for the Future raises a number of questions that can help us reconsider our attitudes to collections. 'Is there a serious expertise deficit?' asks the document. Yes, there is. And even worse, there is a complacent acceptance of ignorance. Too often, I encounter museum administrators who openly profess that they know nothing about 'their' collections, curators who do not think it important to find out who made an object or why it was made or what it was for.

Museum careers now seldom offer either time or place for the long, slow acquisition of knowledge. Mobility is held up as a good thing in itself. But whether of function or place, mobility is not readily compatible with profound knowledge of a collection or a subject. And yet it is the communication of knowledge that brings collections alive, that creates the insights that live on in visitors' minds.

It is respect for the devoted acquisition of knowledge that makes museums the sacred spaces to which communities and individuals will entrust their treasures.

We really must ask ourselves why, if we regard knowledge as important, we have progressively demoted specialist curatorship, both in status and in salary. If we respect the importance of knowledge and if we want a wide range of able people to come into museums to acquire it, then we must pay for it. mj