The bane of PhD students– the General Discussion

This year has been a bit of a bumper PhD submission year for me, five of my PhD students have come to the end of their time, and have submitted, or will soon be submitting their theses.  In my experience, 48 successful students and counting, it is relatively easy to reassure PhD students that their worries about the structure of their thesis, the appropriateness of their analysis and how many tables and figures they should have, are not justified. Many of them already have papers in print or in press by the writing-up stage so they only need a little bit of reassurance about the quality of their work.  The bit that seems to worry them most is the General Discussion.  My advice to them was, and is, the same as that given to me by my supervisor 37 years ago, “spread your wings, sell your work, don’t be afraid to speculate a little, enjoy yourself and make sure you don’t just summarise your thesis”. 

This uncertainty about how to handle the General Discussion is not just a foible of my students.  My impression over the last few years, borne out by the increasing frequency on which I comment on the shortcomings of the General Discussion of the PhD theses that I examine (now more than sixty) is that General Discussions are not what they used to be.  I too often find myself reading a series of lightly edited chapter abstracts, which in my opinion is not a General Discussion. Am I, however, suffering from grumpy old git syndrome or were General Discussions more general in the days of my youth?  How for example, does my General Discussion stack up compared with that of the modern-day PhD student? Did I practice what I now preach?

I do of course still have a copy of my thesis (Leather, 1980), two to be precise. Both my parents were biologists, albeit botanists, so I felt obliged to give them a copy, which I retrieved when clearing my Mother’s house after her death.  The upshot being that I have no excuse for not being able to find a copy from which to do a critical appraisal of my General Discussion. My thesis was written before Word Processors existed, and when computers occupied their own buildings. It was typewritten (by me using a Silver Reed A3 typewriter) and so no electronic copies are available.  As a consequence, I have had to scan the parts relevant to my story; hence the poor quality of the illustrations 🙂

At this point, I should point out that although I was trained as an agricultural entomologist and my PhD was about an agricultural pest, the bird cherry-oat aphid, my supervisor, Tony Dixon, was and still is, an ecologist.  Our lab was thus a mixture of pure and applied ecologists, some of whom weren’t even entomologists 🙂 This meant that I was exposed to a wider range of ideas than if I had just been in a lab of only applied entomologists.  Despite not being overly mathematical or theoretically inclined, I’m pretty much an empirical ecologist (field and lab), I was very impressed by the late, great E.C. Pielou, to the extent that I bought her book Ecological Diversity and read it cover to cover*.  Working with a host alternating aphid, I immediately latched on to her definition of seasonality as being synonymous with environmental variability (Pielou, 1975) and decided to coin a new term, seasonability** .

An excellent start, the title page doesn’t even mention the words General Discussion 🙂


I defined seasonability as being “the pre-programmed response to predictable environmental change” in  my terms this meant that the organism, in this case my aphid, anticipates the trend in conditions, something I, and a more mathematically inclined colleague did actually show a couple of years later (Ward et al., 1984).  I then drew the analogy that an aphid clone could be equated with Harper’s visualisation of a plant being constructed of a series of genetically identical modular units (Harper, 1977), i.e. each individual within the clone, although being genetically identical has a specific (and seasonal) function I also managed to slip in a reference to my other ecological hero, Dan Janzen at this point (Janzen, 1977) 🙂

I see that I was keen to introduce new terms, as my second figure shows.  I was amused to see in figure legend that I describe the x-axis as food quality but label it as host quality in the

A pretty lousy figure, but remember we had to draw our figures by hand in those days. Here I attempt to coin another new usage, this time refluence, to indicate the flowing back of the clone to the primary host.

figure, doing something that in later years I have waxed wrathfully against (Leather & Awmack, 1998; Awmack & Leather, 2002).  In this case, food (nutritional) quality is the term I should have used although I could argue that the build-up of natural enemies on the secondary grassy hosts and the predictable absence of natural enemies on the primary host, could justify the use of the term host quality, but that would be post hoc sophistry and best avoided 🙂

I was obviously also very keen to introduce new meanings to words as my third figure shows.

Yet another attempt to coin a new meaning for an existing word


At no point however, did I summarise what was in each chapter.  I referred in passing to one…”It is now fairly certain from the evidence presented on the effects of growth stage (Chapter 4) that..” and the four figures are unique to my General Discussion, even the two that contained data points, so I can pat myself on the back in that respect.  Although I did not extend my discussion to other taxa, I did range far and wide across the aphid world so I think that fulfilled the brief of spreading my wings, and boy did I try and sell my work.

I also notice that the 25-year-old me tried very hard to use a different sort of language in his General Discussion such as, “lends further credence to the concept of seasonability” which is followed in the next sentence by “..when the bursting of the buds of the tree host or resurgence of sap in the perennial herbaceous host, herald the start of egg hatch”. Yes, I actually used the word herald, but then, this is the guy who prefaced his thesis with these two quotes.

The Steinbeck quote (Doc from Sweet Thursday, does still sums up pretty much what I want to do with my life.


So what does the 62-year-old Professor of Entomology think about the efforts of his younger self?  I may be slightly biased, but I think it is a reasonable effort and as an examiner I wouldn’t have any major problems with it although I suspect that I would be tempted to have a gentle dig at the attempts to coin new terms. Overall I would rate it as B+.

In case you wondered , although I never published, or even tried to publish my General Discussion, all the ideas, except for the terms which were petty awful, (or naff as we would say in the UK), have made it into print at some time.

To reiterate, my advice to PhD students struggling with your General Discussion is “spread your wings, be bold, sell your work, don’t be afraid to speculate a little, enjoy yourself and most importantly,  definitely make sure you don’t just summarise your thesis”


Awmack, C.S. & Leather, S.R. (2002) Host plant quality and fecundity in herbivorous insects. Annual Review of Entomology, 47, 817-844.

Leather, S.R. (1980)  Aspects of the Ecology of the Ecology of the Bird Cherry-Oat Aphid, Rhopalosiphum padi (L.).  Unpublished PhD Thesis, University of East Anglia, Norwich.

Leather, S.R. & Awmack, C.S. (1998). The effects of qualitative changes of individuals in the population dynamics of insects. In Insect Populations In Theory and in Practice (ed. by J.P. Dempster & I.F.G. McLean), pp. 187-206. Kluwer, Dordrecht.

Harper, J.L. (1977) Plant Population Biology, Academic Press, London.

Janzen, D. H. (1977) What are dandelions and aphids? American Naturalist, 111, 586-589.

Pielou, E.C. (1975) Ecological Diversity, John Wiley & Sons Inc., New York.

Ward, S.A., Leather, S.R., & Dixon, A.F.G. (1984) Temperature prediction and the timing of sex in aphids. Oecologia, 62, 230-233.


*I also bought her book Mathematical Ecology but didn’t manage to read it cover to cover 🙂

**I had great hopes of getting my General Discussion published and my new term being adopted by ecologists around the world 🙂



Filed under Science writing, Teaching matters

7 responses to “The bane of PhD students– the General Discussion

  1. Simon

    I didn’t get away with ‘festooned’ (in an earlier chapter). If you can’t wax lyrical in an unpublishable section of something no-one will ever read, where can you…

    Liked by 1 person

  2. Nice post. In Australia, the final chapter is often called the Synthesis, which should be a bit of a hint as to its intended content. But some students still need a nudge to move beyond the summary of chapters.

    Liked by 2 people

  3. Tom Fairman

    I guess my main question is – do you recommend or caution against opening your thesis with some poetry?


    • I think that whatever comes before the actual thesis content is like the acknowledgements pretty much free-flow and allowable. I have seen quotes from all sorts of sources, so if there is something that you feel expresses your feelings, go for it 🙂


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