All that remains is to summarize what this excavation has uncovered, and in the process to undermine the assumption that the foundational conditions of rules and fiction do not also offer an aesthetic value judgement. Unsurprisingly, we have collected an extremely diverse set of value judgements – what if anything unites them? As philosopher Mary Midgley remarked in her 1974 paper "The Game Game", there is a unity in concepts like 'art' and 'game' simply "because they all deal with human needs, which certainly do have a structure". In “The Neurobiology of Play”, I attempted to provide a foundation for this structure by considering human neurobiology, and in an attempt to make sense of the disparate aesthetic positions there may be no clearer place to start than the underlying biology.

One of the core patterns that we associate with play is that which involves the pursuit of triumph (Ekman's fiero), which I hypothesise is a large release of the reward chemical dopamine. In the victory aesthetic offered by Crawford, Costikyan, Koster and many others, this is the biological foundation that is most clearly expressed. To reach the particularly strong pay-offs in terms of triumph, it is usually necessary (as Nicole Lazzaro has observed) for the player to become frustrated i.e. to become angry. This is to push the fight-or-flight response firmly into 'fight' – and fighting is what the victory aesthetic stresses.

In its refined form as the conflict aesthetic, the fighting becomes embodied as battle – which some (such as Crawford) place as the highest condition of a game. In both victory and conflict, there is a necessity for the player to endure frustration in order to reach the most intense reward states and this almost certainly relates to testosterone, which has a demonstrated role in persistence. I want to suggest, therefore, that the victory aesthetic and testosterone go together – and that the conflict aesthetic is merely a refinement of the general formula expressed by the victory aesthetic. Because testosterone and pugnaciousness go together, this may also explain why advocates of victory or conflict aesthetics are so forceful in defending their definitions of games as necessarily true.

However, the experience of triumph can also be reached not by enduring frustration, but by enduring boredom or confusion – being compelled by curiosity and the promise of eventual reward to find a solution to a challenge by viewing it as a problem. The problem aesthetic espoused by Costikyan and others is thus a twin to the victory aesthetic – the same experience is prioritised ('triumph over adversity' or fiero), but the route to it is different. (The reward aesthetic, found in McGonigal and the early Bateman and Boon, can be seen as a weakened from of the victory or problem aesthetics – the same kind of biological reward systems are in play, but endurance in the face of frustration, boredom or confusion is not assumed.) 

What is different biologically in the case of the problem aesthetic is the operation of the decision centre of the brain, the orbito-frontal cortex. This region – which is closely linked to the region responsible for the release of large amounts of dopamine – is closely connected with decision-making and problem solving (e.g. Franken et al, 2005), and also releases smaller amounts of dopamine in expectation of future reward. In other words, if the orbito-frontal cortex predicts that a problem can be solved, the individual receives a hit of dopamine to encourage them to continue. Just as the conflict aesthetic was seen as a refinement of the victory aesthetic, the decision aesthetic is simply a refinement of the problem aesthetic focussing on the decision making, and the learning aesthetic found in Koster and Cook is a refinement of the problem aesthetic that looks over the long-term to what accumulates, rather than to the individual problems in isolation.

It is possible testosterone is also involved in this problem(-decision-learning) aesthetic approach to play – some further empirical testing would be required to determine this. If it does still relate to testosterone, this would explain why defenders of the problem aesthetic are as confrontational as proponents of the victory aesthetic, but there could be other explanations. Strong activation of the orbito-frontal cortex appears to be the "biology of nerdhood", which is psychologically expressed in the Rational archetype in Temperament Theory, or in Simon Baron-Cohen's concept of a systemizing brain or S-brain (as opposed to an empathic brain, or E-brain). The S-brain (which Baron-Cohen also considers a "male brain", while recognising that both men and women can have this kind of neurology) is constantly systemizing the world, that is, it expresses "the drive to understand a system and build one". This connects the problem aesthetic to the systems aesthetic, and explains why advocates of one often support the other: when people view the world as systems, perceiving challenges as problem-solving is the obvious corollary. It is small wonder that exponents of this viewpoint often fervantly claim that everything is a puzzle to be solved!

Furthermore, the systems aesthetic is not just a nuanced variation of the problem aesthetic – it corresponds to the desire to view games in terms of rules. Only when games are seen as formal systems (though the S-brain perspective) is the rule-element of games likely to be emphasised, and with this in mind we can now remove the foundational status of rules. Yes, rules are always there to be found – but only when games are seen primarily as systems. There is no explicit rule aesthetic, as such, but the system aesthetic (and the problem aesthetic it refines) were always intimately connected with the perspective of games as rule systems. This is the entire perspective collected under the term 'ludology', as captured by Ian Bogost's remark that the ludology-narratology debate seemed to be the question: "Is a game a system or rules, or is a game a kind of narrative?", but would have been better expressed by the question: "Is a game a system of rules, like a story is a system of narration?" Both ludology and narratology stressed the system-aspect – ludology just made 'rules' the central focus.

Just as the foundational status of rules pairs with the systems aesthetic, the narratologist's fascination with fiction pairs with the imaginative aesthetic foreshadowed by Costikyan and espoused directly by me in Imaginary Games (2011), albeit constrained once again by the systems aesthetic. The systems aesthetic thus bridges between fiction and rules, and hence between the problem aesthetic and the imaginative aesthetic. Just as the rules can always be found provided a systems-perspective is applied, so too can the fiction always be elucidated provided one comes to the situation with a model of fiction (like Walton's make-believe theory of representation). However, there is a huge gulf between the problem aesthetic (with its goal-oriented, outcome-focussed attitude) and the imaginative aesthetic (with its process-oriented focus on story and inventiveness). The agency aesthetic offered by Crawford may fit under or near the imaginative aesthetic, as a refinement of it that pulls back towards the problem-aesthetic via the emphasis on decisions the player makes. Perhaps the decision and agency aesthetics would be best seen as bridges between the problem aesthetic and the imaginative aesthetic. The curiosity aesthetic may also have this dual identity: it part-fuels the desire to solve problems, but it also powers a compelling interest in "richly interpretable" fictional worlds.

Another of the aesthetics brought in tangentially by Costikyan probably deserves far more attention than it has currently received: the social aesthetic. Because so few game designers or academics have drawn explicit attention to it in their definition of a 'game', it is difficult to do this value judgement justice. However, in my studies of players it is clear to me that there are a great many for whom the social rewards of play are a significantly greater draw towards games than victory or problems. The fact it is not clearly represented in this brief survey of game definitions almost certainly reflects the systemising perspective described by Baron-Cohen: it is the nature of the S-brain perspective to build systems, and the nature of the E-brain to view situations in terms of people's emotional states. The social aesthetic is expressly about this empathic approach to play, and the literature is sparse on it precisely because the systems aesthetic drowns it out. There is a small hint of it in the social abusive play recognised by Doug Wilson and Miguel Sicart, but even this is buried under their wider conception of abusive play, which is primarily an extreme form of the testosterone-fuelled victory aesthetic.

Finally, the uncertainty aesthetic found in Caillios and Malaby comes at games from perhaps as wide a perspective as is possible. All the previously described aesthetics could potentially be subsumed under its vast tent, and the playful aesthetic of Huzinga, Suits and others can be seen as a refinement of it. Perhaps the voluntary aesthetic advocated by Caillois, Suits and McGonigal could also be seen as a refinement of the uncertainty aesthetic, if it does not transpire to be a refinement of the social aesthetic instead. The putative mastery aesthetic, found in players but not obviously expressed in definitions of games (although Cook comes exceptionally close to doing so!) might also be a refinement of the uncertainty aesthetic, or perhaps a bridge between it and the victory aesthetic. The trouble with viewing specific aesthetics as refinements of the uncertainty aesthetic is precisely the scope of uncertainty to subsume anything under its remit.

As a metaphor to capture this arrangement of the aesthetics of play, imagine a tall twin-peaked mountain, rising high above a lone village upon a forested island amidst a vast uncharted sea. The twin peaks of the mountain are the intense rewards of triumph offered by the victory(-conflict) aesthetic and the problem(-decision-systems-learning) aesthetic, while its foothills are the more modest and accessible charms of the reward aesthetic. Here, in the lower slopes, the mysterious forest stands for the imaginative(-agency-curiosity) aesthetic, and the village for the social aesthetic. The sea that surrounds the island is the uncertainty(-voluntary-playful) aesthetic, within which all kinds of play and games can be found.

Whether or not this is a complete description of the landscape of the aesthetics of play remains to be seen, but whatever the case this approach to studying games offers a potential liberation from the interminable fight over the positions of boundary fences.

More game aesthetics soon!