Evaluation and dialogue:
An "impossibility" result


The core concept of the paper is an "argument", a statement which establishes the priority of planning alternatives. The ideal of Habermasian dialogue is an important theoretical reference point in communicative planning and can be seen as an informal way of pooling arguments. This pooling is called a "dialogical" decision-making procedure and it follows certain ethical and democratic rules. Some requirements that seem reasonable when trying to make a "dialogical", collective decision are specified below. However, the impossibility of simultaneously fulfilling these requirements is evident when an analogy is drawn with Arrow's general "impossibility" theorem of social choice. When adapted to "dialogical" decision-making, the theorem states that:

no "dialogical" decision-making procedure can combine non-dominance, the Pareto principle, unrestricted domain, and the independent nature of irrelevant alternatives when arbitrary planning decisions, made on a cyclical basis, are not accepted.

The four requirements are defined as follows:

  • the "dialogical" decision-making procedure should not give one particular argument priority, no matter what other arguments are put forward in the debate ( ie. non-dominance, or non-dictatorship)
  • when all the arguments suggest that one planning alternative is the winner, the "dialogical" decision-making procedure should not have regard to other alternatives (Pareto principle)
  • the "dialogical" decision-making procedure should be able to pool any number of arguments, no matter how each argument ranks the planning alternatives (unrestricted domain)
  • this procedure for pooling arguments should only take into account each argument's ranking of the planning alternatives and exclude all other information (independence of irrelevant alternatives).

The latter requirement shows that the theorem of impossibility is valid only for planning debates concerning goals or effects measured on an ordinal scale (ie. the existing information allows for prioritising, but is insufficient to establish differences or ratios between the planning alternatives.)

Each item in an environmental impact assessment (EIA) or a formal "ex ante" evaluation technique can be regarded as an argument. When setting priorities such techniques imply a formal pooling of arguments. Several evaluation techniques for land-use planning and transport planning can be used for handling effects measured on an ordinal scale, for example, Lichfield's community impact evaluation (the planning balance sheet) and Hill's goals achievement matrix. The assessment of environmental plans, e.g. urban green structure, often relies on variables that are hard to quantify, such as visual quality and the long-term effects on human health. This inconsistency proves that the formal pooling of arguments in the evaluation of such plans disregards assumptions that are reasonable in public deliberation.

The paper links formal evaluation and communicative planning and shows both that ways of amalgamating arguments and setting priorities among planning alternatives which have intangible implications are up against an "impossible" result of the Arrow principle.

This paper will appear elsewhere in full during 2000 - contact author

Tore Sager
Norwegian University of Science and Technology, NTNU

Communication in
Urban Planning

Göteborg Conference Papers - Oct 1999

Workshops for Environmental Innovations (Eijk et al)

Communication and Urban Green (Lindholm)

Integrating Biodiversity (Gyllin)

User participation in Public Park Administration (Delshammer)

Making Outdoor Places for Children (Kylin)

The Home Street (Staffans)

Identification of ecological potentials (Guldager et al)

Evaluation and Dialogue (Sager)

A Communicative Planning Methodology (Stromberg)

Rationality Revisited (Lapintie)

Planning deconstructed and rebuilt as discourse analyses


"Whereof one cannot speak, thereof one must be silent"





European Research Network - Urban density and Green Structure

Proceedings of the Gothenburg Conference:
Communication in Urban Planning - Oct 1999

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