Our writing partnership in philosophy began in 2007, when Anjum arrived at Nottingham as a postdoctoral fellow. Since then, we have written three books and about 40 papers together, which seems rare, especially in philosophy.

We think it¡¯s time to issue a statement about our writing partnership, for at least four reasons.

First, we want to make it clear that ours is an equal partnership and we take 50 per cent credit each for everything we publish together. We decided early on to go with Mumford-Anjum for author order and now we stick with it for consistency.

Second, people have been curious about how we work together, especially as we live in different countries.

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Third, we are aware that co-authorship is still treated with some suspicion, of which both of us at different times have been victims.

Finally, we want to advocate in favour of co-authorship and explain some of the considerable benefits we find in working together.

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A little more can be said about the third point, for we both feel there have been occasions where we have suffered from having written together. There have been different times when credit for the work was withheld from us both, based on a view that it was the other who did most of it.

There was even a case where we had a third co-author and not one of the three of us was allowed to claim credit for the paper.

Somebody must be writing these papers, however. It seems all too easy to point a finger at any one of the authors and suggest they did not pull their weight. That would be nothing more than presumption, and one that has little basis in the reality that we know.

The process

We hope to clear up some of these misconceptions by describing how we work together.

People often ask who wrote which part, but this is the wrong question. The first thing we would say is that it is an extended process and the more we have written together the more we have learned how to conduct it. It now operates pretty smoothly although it took us a while to reach this point.

We use the Mumford Method of writing, which has been explained elsewhere and we will not detail it here too much. This method has several stages, all of which we regard as collaborative.

First there is the discussion. We have found this is always best face-to-face. It is thus the activity we prioritise for the occasions when we are together. We are often motivated by some problem or question and find that when we discuss it, one of us comes up with an interesting point.

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It is then a bit like a tennis match, with a time of back and forth, which leads to the idea undergoing a rapid development. It gets challenged and tested quickly. There are sometimes big arguments as we are both stubborn and want to find the right answers.

Someone once told us that co-authoring works best with about 20 degrees of disagreement. We think this is about right and it describes what we have. If you disagree on everything, you cannot work together. It you disagree on nothing, there¡¯s no point.

We agree over many of the fundamentals ¨C such as the reality of causal powers ¨C but there is enough friction over the details to ensure that any new thesis gets scrutinised adequately and developed before it is either accepted or rejected.

After some time at this, we reach a point where we can summarise our agreed view in a Mumford Method plan. As we are both practised at this, either one of us can put together a sketch of a paper very quickly.

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Then, as is standard for the method, it undergoes several rounds of revision, back and forth again, and bringing in any input we receive from presenting talks. We will also share out any research that is necessary at this stage, reading essential sources that have been brought to our attention.

Only when we are satisfied that the plan is ready is an initial draft paper produced, sometimes a few years after the first discussion. Either of us can do this first draft. Sometimes this is determined by which of us has the most free time on their hands or who is most keen to get the paper finished. This is followed by us each going over the draft in detail, making tiny corrections so that the paper reads smoothly and as if it was written effortlessly.

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We have a strict rule that nothing goes into the finished version unless we both agree. We in effect operate a veto system. This has sometimes led to our biggest disagreements when we have spent hours arguing over one sentence or even a single word. If we really cannot agree, then the part in question comes out and we avoid the topic. We find, however, that if we return to a contentious matter after a long gap, there is sometimes a way to agree after all.

A misconception some seem to have about our writing is that it is multi-authored rather than genuinely co-authored.

It is not that we divide the sections or chapters between us to write in isolation. We really cannot say who did what. Our finished product is like scrambled eggs. Once they are made, you cannot recover the individual eggs that were put in.

Indeed, we think of our finished product as a lot more than a sum of individually contributed parts.

The benefits

This brings us to the benefits. When you go through such a long process, occasionally involving some drama, and then also find that there can be a distrust of your co-authored result, you need to be very sure that you are getting more benefit from the collaboration than it costs.

In the case of our partnership, we think the benefits are considerable. We see the process as involving some kind of non-linear interaction, resulting in a finished product that is far better than either of us could have produced alone.

There are massive gains in creativity and productivity and we feel that there is no end to the ideas once we meet. They are often queuing up, waiting to be drafted. We have never thought that, as a team, we could dry up.

There is sometimes a thought in the arts that progress is to be made through a solitary struggle. Single authorship is still standard.

But it is very hard for new ideas to come and be developed when sitting alone. We make progress much quicker because when one of us gives voice to a new idea, the other picks it up and runs with it before giving it back. We each have our own foibles, interests and personalities, which means that something new is added to the other¡¯s point. There¡¯s a little bit of yin and yang.

The whole collaboration process is rewarding, enjoyable and a lot of fun. Even if it was nothing but pain, it would still be justified on intellectual grounds alone.

Fortunately, the work has never failed to be satisfying and we hope this answers the sceptics.

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Stephen Mumford is professor of metaphysics and executive dean of the Faculty of Arts at the University of Nottingham. Rani Lill Anjum is research fellow in philosophy at the Norwegian University of Life Sciences. This post on the blog Rani blogs about causation etc.