On Assumptions V

"Pick the assumptions to pieces till the stuff they are made of is exposed to plain view - this is the cardinal rule for understanding the basis of our beliefs." (Eric T Bell, "The Search for Truth", 1934)

"No step should ever be taken, and no statement should ever be made, without giving a legitimate reason therefor. A 'legitimate' reason means a reference to a definition, to an assumption, or to a proposition previously proved; it may also include reference to a statement in the hypothesis, or to a line arbitrarily drawn at the outset of the demonstration." (William L Schaaf, "Plane and solid geometry for home study", 1944)

"Whenever we discuss a geometric statement in order to prove it, we refer to previously proved statements for 'evidence'. In this process of referring back to earlier statements that have already been established by proof, it is clear that some few of the earliest statements must of necessity remain unproved - that is, they have to be taken for granted, since we must begin our chain of reasoning somewhere. It is not possible to prove every statement. Those statements which are thus taken for granted without proof are called assumptions. Hence in all logical reasoning, two considerations are of prime importance: (1) the meanings of the terms used, and (2) the basic assumptions made." (William L Schaaf, "Plane and solid geometry for home study", 1944)

"A bad model is a combination of assertions, some factual, others conjectural, and others plainly false but convenient. [..]  By definition, a bad model does not give power to see-accurately, deeply, or at all-into the actual situation, but only into the assertions embodied in the model. Thus, if the use of a bad model provides insight, it does so not by revealing truth about the world but by revealing its own assumptions and thereby causing its user to go learn something about the world." (James S Hodges, "Six (or So) Things You Can Do with a Bad Model", 1991)

"In everyday language, an axiom is often held to be a 'self-evident truth'. That phrase betrays some awfully sloppy thinking. A truth can be evident, but self-evident? Evidence is what convinces people that something is true. So what on earth is 'self-evident' supposed to mean? A truth that convinces itself? [...] To those who were seeking foundations for mathematics, axioms were much more prosaic. They weren't truths at all, let alone evident ones, and certainly not self-evident ones - assuming that such a slogan means anything at all. Axioms were assumptions. A place to start. A collection of statements that mathematicians agreed to accept. You are free to challenge them if you wish, but even if you do, you won't change mathematics (though you might create some more, branching off in a new direction). From the axiomatic viewpoint, mathematics consists of the deductions that are made, once the axioms are accepted as a starting point. It's like a game. If you want to play football, then you follow the rules of football. Of course you are free to change the rules - but then you're playing a different game." (Ian Stewart, "The Magical Maze: Seeing the world through mathematical eyes", 1997)

"When people question assumptions, the map may clarify what they are. When logic is challenged, the map may help. When people want to know how goals and strategies are linked, the map may show how they are. The map does not make the decisions. Rather, it provides a record that preserves complexity, yet organizes and categorizes that complexity in such a way that people can understand and manage it. And if more mapping needs to be done, the map is there as a base on which to build." (John M Bryson et al, "Visible Thinking: Unlocking Causal Mapping For Practical Business Results", 2004)