Least dangerous assumption

The 'criterion of the least dangerous assumption' encapsulates an orientation to Pedagogy. It holds that, 'in the absence of conclusive data educational decisions should be based on assumptions which, if incorrect, will have the least dangerous effect on the student'.. The principle is most closely associated with the areas of intellectual disability and communication disorder, although it can be argued to have a more general relevance in the domain of learning and teaching, and beyond. In most contexts in which it is used the principle can be taken to mean that one should, in the absence of evidence to the contrary, presume competence in others, rather than non-competence.

The 'presumption of competence' can be regarded as the 'least dangerous' assumption to make about a person because it is arguably less damaging to presume competence in another, and to be wrong, than it is to presume non-competence (incompetence) in another, and to be wrong. Take the example of a teacher who is uncertain about the extent to which a student understands what is being said to them. The principle holds that it is less 'dangerous' to assume that the student understands everything that you say to them, and to be wrong about that, than to assume that the student understands nothing that you say, and to be wrong in that direction. The reason (so the argument goes) that the latter is more dangerous than the former is that under the latter assumption the teacher is likely to speak too little to the student (or, in an extreme form of the argument, may not speak to the student al all), which is, arguably, worse than the teacher speaking too much to the student.

It is essential, when evaluating the worth of this principle (in particular with regards to its implications for practice) to note the precondition for its relevance: 'in the absence of conclusive data...'. Those practitioners who hold to this principle are not in favour of being wrong about a student's competence. It is much, much better (much less dangerous) to be right about this in the first place. The principle comes into play under conditions of uncertainty. It is a starting point for practice when there simply is not enough evidence to go on, in estimating the competence of a student. It is under those conditions that one might argue that presuming competence is less dangerous than presuming non-competence.

Needless to say, whilst one might acknowledge the abstract logic of the argument put forward by its proponents, as soon as a principle such as this meets the complexity of everyday practice, it rightly becomes the subject of intense critical debate. Much of that debate revolves, in effect, around what constitutes 'conclusive data', given how difficult it can be to make the correct inferences about underlying competence, on the basis of assessments of performance.

Notwithstanding the critiques, this rule of thumb, when thoughtfully applied, encapsulates many principles of 'good teaching practice'. For example, as Donnellan argues, 'the criterion of the least dangerous assumption holds that there is less danger to students if teachers assume instructional failure is due to instructional inadequacy rather than to student deficits'. One might argue that this is a constructive place for teachers to start, when evaluating their own practice. If a student is failing to learn a thing, and one wants to diagnose why that is happening, it is appropriate to consider whether there are other ways of going about the teaching of that thing.