When a newly arrived dean asked if I would be her mentor, I was surprised and flattered - but a little taken aback. Since she was already formidably experienced, what on earth could I do for her other than remind her of the photocopying policy or what to do about students smoking in the toilet?

The official guide for good mentors that I tracked down on the web didn't offer much enlightenment. A mentor, it advised, "is that person who achieves a one-to-one developmental relationship with a learner; and one whom the learner identifies as having enabled personal growth". To be effective, apparently, I would have to commit time and effort, provide regular bilateral interface and, crucially, keep a log of experiences and progress.

It's all a far cry from the original meaning of the term, which has its roots in Homer's Odyssey. When Odysseus, king of Ithaca, went to fight in the Trojan War, he left his trusted friend Mentor to act as a teacher and overseer to Telemachus, his son. Eventually the goddess Athena took the disguise of Mentor to encourage Telemachus to go and find his father. Accompanying him through deadly hazards and encounters with ruthless enemies, she may not have been aware of the expectation, outlined in my guide, that she should help the young prince "engage with major career transitions or work in environments subject to major organisational change".

Neither would Aristotle, who mentored Alexander the Great, nor Johann Christian Bach, who did the same for Mozart, have thought much about the importance of managerial tutelage in the context of their developmental alliance. And there's little evidence of "learner-centred engagement to facilitate personal growth" in the mentoring process documented in Tracy Chevalier's new novel. Remarkable Creatures is based on the relationship between the fossil collector Mary Anning and the older, more worldly Elizabeth Philpot in the early 19th century. Mary, from a struggling working-class family in Lyme Regis, uncovered a number of previously unknown species, some of them gigantic, which she managed to salvage and restore, accumulating an astonishing wealth of knowledge despite having no access to the worlds of science or society.

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Elizabeth, from a genteel family in straitened circumstances, came to live in Lyme Regis with her sisters and quickly developed an intimacy with the younger girl. Theirs was not an arrangement that bore much affinity with my mentoring guide. Rather than establishing set procedures, itemising goals and agreeing a staff-development plan, they would meet on the beach most days. Nothing was logged except for the dates and locations of their discoveries. Instead they would hitch their skirts as they clambered over the rocks, braving gusty gales in the search for unfamiliar protuberances or strange markings in the cliffs. Mostly they talked and dug.

But in one respect their relationship did match the recommendations. They both learnt from each other in what the guide approvingly calls a "two-way street" - a term that has become somewhat tarnished since its adoption as a catchphrase by one of cinema's more treacherous mentors, Katharine Parker, played by Sigourney Weaver in Working Girl. Promising her secretary, played by Melanie Griffith, a supportive partnership based on trust, she proceeds to steal her ideas and block her promotion, blatantly ignoring the guide's warning to avoid "role-strain as a result of inappropriate role use, which could impact on the quality and outcomes of the relationship".

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And Katharine is just one of a legion of faulty mentors in fiction. There's Voltaire's relentlessly sunny Pangloss, whose efforts blind rather than enlighten his pupil Candide, or sinister Madame Merle, who besmirches the innocence of Isabel Archer in Henry James' The Portrait of a Lady. Neither bothered to ensure that their subjects were encouraged to "self-reflection through the establishment of well-developed feedback loops".

In Jane Austen's Emma, currently being serialised by the BBC, it's the heroine herself who proves to be a less than ideal mentor. Rich, spoiled Emma Woodhouse, who creates havoc and near disaster when she takes under her wing the pretty but dim Harriet Smith, had clearly never read the good mentoring code, which insists that you must guide but never control. Emma's not much of a listener and, in clear breach of the guide's precepts, prefers to impose her own views wherever possible.

Maybe I'm a closet Emma myself, which probably explains why I haven't adhered terribly faithfully to the mentoring rules either. My fellow dean and I haven't written down any objectives, nor have we monitored her progress in relation to these. Our meetings have no agenda and no formal venue, the only consistency being the involvement of gin and tonic. Advice about devising an employability strategy or managing the catering service lasted for about two sessions.

These days we're still on the gin and tonics, but we've slid into a different pattern. In blatant contravention of the mentoring rules, I'll tell her to get tough with a whingeing colleague or take the odd reckless gamble, while she'll assess sternly how far my latest outburst in academic council might be construed as a career-limiting intervention. We'll definitely tell each other if our bums look big in this or that.

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I'm still working out how to enter that one in my mentoring log.