The debate about entry to higher education is important to anyone who cares about fairness. A degree offers no guarantees these days but it can still be a passport to a better life, especially if the certificate carries the crest of one of the elite institutions. It is therefore imperative that we have a fair admissions system to HE.

The debates about whether American-style aptitude tests or A-levels are best, or whether universities should accept students from poorer backgrounds with lower grades, rarely grapple with the fundamental issue of what fairness means. But then philosophers have been grappling with that issue for millennia, without providing a definitive answer.

But we don’t need to solve this eternal conundrum to gain some much-needed clarity. For on reflection, it is not hard to piece together the bare bones of what constitutes fairness in this context. Broadly speaking, a fair system will give university places to those best placed to make the most of the opportunity and whose records suggest they deserve them.

A-levels offer a crude way of determining whether these conditions have been met. Students do not compete on a level playing field. Going to one of the best schools and having a supportive, educated family background gives a student a head start on their less-privileged peers worth at least a couple of grades. Their results exaggerate both the scale of their achievements and their potential to excel at degree level.

For that reason, there is increasing talk of introducing an American-style scholastic assessment test, which confusingly shares an acronym with our own very different Sats. The US-style Sat is supposed to provide an objective measure of aptitude, rather like an IQ test. But even if we assume what some deny - that you can measure general intellectual ability - the Sat alone would not deliver a fair university entry system.

A greater innate ability than someone else does not mean a person deserves a better education. Virtues such as application, determination and effort are also part of the equation. It would be grossly unfair if a student worked hard to surpass herself and then found that a cleverer wastrel took her place at Oxford, simply because a test showed she were more intelligent. The criteria of merit demands that we look at more than just raw ability.

The same reasoning applies when we consider the requirement that places go to those best placed to make the most of them. A cleverer student is not necessarily the one best able to make the most of their educational opportunities. The example here should be David Beckham, not Paul Gascoigne. The latter had the greater innate ability, but Beckham both achieved and deserved greater success because he made the most of his talents rather than frittering them away.

It seems then that neither A-levels nor the Sat provide a fair means of assessing where university places should be allocated. What is needed is a way to balance actual and potential achievement - innate ability and how far students excel themselves or let themselves down. Only by combining the information provided by exams, aptitude tests and a sensitivity to the student’s background can a full picture be built.

This three-pronged approach may be too complex. In which case, the best compromise is simply A-levels or their equivalent, discounted to allow for the effects of social and economic advantage or disadvantage.

This is more-or-less what Bristol university did, only to find itself accused of social engineering. The criticism is wide of the mark. The policy is not about increasing admissions from poorer social backgrounds for its own sake, but to reward those whose efforts and abilities make them best suited to receive the advantages of HE.

Anyone who thinks that we should admit students solely on either the Sat or A-levels has not thought hard enough about what fairness demands.

Julian Baggini is editor of The Philosophers’ Magazine