What is a Proposition?
A proposition is a claim. A logical proposition may be written using formal or informal logic.
Formal logic began with the 'syllogism'. A syllogism is a series of premises and a conclusion. This may be deductive or inductive (and there are other varieties as well). The famous case being 'Socrates is a man. All men are mortal. Therefore, Socrates is mortal.' In this case, if the two premises are true the 'form' of the argument guarantees the truth of the third statement or conclusion. No new information is created. That is, if Socrates is a man and all men are mortal then it follows with certainty that Socrates is mortal. This is deductive logic. In deductive logic, a valid proposition is 'truth preserving'. This means if the premises are all true then the conclusion is also true.
Informal logic is more easily recognised in arguments that occur in everyday life. Originally this was the domain of 'rhetoric' (discussed further in the next section below). This included arguments about whether so and so is a good actor (epideictic rhetoric), or who was responsible for committing some crime (judicial rhetoric). When focused on arguments about what we should do this was 'deliberative rhetoric'. Contrary to popular belief rhetoric was not (just) about 'tricks' but a serious study concerned with the artful selection and arrangement of premises to lead to a persuasive conclusion. Here the form of the argument is no guarantee of the conclusion. In addition, 'warrants' or reasons need to be provided, fallacies avoided, and assumptions checked. Informal logic is very useful to evaluators presenting evaluation findings. Rhetoric and informal logic is not our focus.
Propositional Evaluation is concerned with formal deductive logic. The form of the argument should guarantee the outcome IF each premise were certain. But, of course, each premise is uncertain. It may seem counterintuitive to demand logical rigour in an uncertain world. Much useful evaluation is focused on the 'how' and 'for whom' that each condition or premise holds in reality. But Propositional Evaluation is focused on whole propositions and not on 'what works for whom under what circumstances'. It's about effective plans, not scientific research.
The motto may be 'we use science, we don't do science'.
Developing a tool to assist people to determine, judge or evaluate whether a proposed course of action is likely to work is the focus of Propositional Evaluation. Propositional Evaluation is not focused on ethics, values or what we should do, but on whether a certain plan or is likely to do what it says it will.
Propositions in the public sphere
A very brief description of the origins of logic in the public sphere
The art of asking and answering questions about the value of action in a world of multiple and interdependent causes and effects is not new. Aristotle called it the art of deliberation; Kant called it practical reasoning. Complexity theory may be new, but the need to deal with complexity is not.
Deliberative rhetoric was, for about 2000 years, the central means for holding a discussion or engaging in 'dialectic' about the value of collective action in an uncertain world. Rhetoric today is synonymous with trickery. This is because rhetoric, the art of speaking, or persuasion includes attention to logos (the word), as well as pathos (emotion), ethos (character) and kratos (timing). Aristotle emphasised the logos and the art of finding the inherent persuasiveness within any given argument.
To this end, Aristotle invented a form of deliberative logic at the start of this period, built around the syllogism of deductive logic. This was called the enthymeme. It differed from deductive logic only in that there were unstated assumptions in the argument AND the premises and conclusions were probable rather than certain. This could be used to develop an argument about the value of a course of action.
Throughout history, the imperative towards reasoning in deliberation was often forgotten in the world of everyday arguments, where winning the argument in an adversarial manner, in a law court, for example, was more important than establishing the best argument. The focus became on debating who was right and who was wrong, rather than ‘dialectic’ or reasoning that was unmotivated, and where the purpose was to end with a better argument than any speaker began with – a productive group discussion if you will. The problem was never with the use of argument, but with its abuse by unscrupulous practitioners.
From Socrates, Plato, and Aristotle through medieval times there was intense debate about the place of deliberative rhetoric and argumentation within a general approach to knowledge. Then as now, the pursuit of 'truth' was the gold standard. This was associated with philosophy and energy was directed towards determining what we could be certain about. This was considered an antidote to mere rhetoric. This position of truth-seeking is now occupied by science. There is less attention in the universities of today for a study of what we may call the ‘uncertain sciences’: with what is reasonable to conclude here and now, rather than with the timeless abstract and certain truths pursued by science.
It may be better to see the focus of Propositional Evaluation through the ancient lens of techne - or knowledge of 'how to do things', rather than episteme, or 'knowledge about things', or in a more modern sense, as concerned with engineering not physics, building things that work (technology) not understanding how things work (science). We love science, but we recognise that we are using it, not doing it.
Why does this matter?
People have always needed a means of making better decisions for collective action in an uncertain world. In the ancient and medieval worlds, there was serious discussion about the art of deliberation.
It is a central claim of Propositional Evaluation that evidence-based public policy today needs a greater focus on sound, valid and well-grounded logic than the development and testing of theory (noting of course that even scientific theories must be evaluated using logic). To support public discourse and democracy we need a greater focus on the art of deliberation and on competing values than any hope that public policy can be practiced based on scientific truth. This begins with acknowledging the rich history in the western and other intellectual traditions of methods for deliberation about the merits of action in an uncertain world that run parallel to the history of philosophy and science.
The possibility of certainty in the western philosophical tradition was demanded by the religious instinct, one reason why ‘truth’ and ‘god’ are so intertwined in the Greek word ‘logos’. See Richard Tarnas' masterpiece 'the passion of the western mind'. Interestingly, the schools of rhetoric and the sophists, in general, were more popular in the ancient world than the schools of philosophy because of their practical utility. Many disagreed with the truth-seeking obsession of the philosophers and their disregard for the utility of rhetoric; some means were required for making decisions in a democracy, in law and for public administration in a world where the standard of certain truth would result in indecision and inaction.
With the triumph of science since the enlightenment and into the modern period we have not been trained in the art of deliberation, seeking instead answers for everything in science. Yet we have a rich intellectual heritage of logic and ethics on which to draw and apply to questions of public policy. Rhetoric is now being rehabilitated as 'critical thinking' as it is recognised that we do need tools for navigating a complex, pluralist and uncertain world where waiting till we find 'the answer' is not good enough and different values are competing for our attention. We need to avoid a single-minded search for what Stephen Toulmin has called 'abstract truths that apply everywhere in general and nowhere in particular.'