In his great work Mathematical Principles of Natural Philosophy, Isaac Newton gave 'four rules of reasoning in philosophy' which promoted parsimony — "Nature is pleased with simplicity, and affects not the pomp of superfluous causes" — and realism:
In experimental philosophy we are to look upon propositions collected by general induction from phenomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions.1If all the 'philosophy' terminology sounds weird, I should point out that 'natural philosophy' was what people called science before they called it science.
Newton's views probably seem entirely reasonable, but there were (and are) radically different approaches to science. You see, philosophers are often very worried about the possibility that our perceptions are misleading about the true nature of reality. George Berkeley 'solved' this problem — in his own estimation — by undercutting an important assumption:
All this Scepticism follows, from our supposing a difference between Things and Ideas, and that the former have a Subsistence without the Mind, or unperceived.2He simply denied that Things exist apart from Ideas, and so skeptics don't have anything to be skeptical about! As a bonus, his solution undercut 'all the impious Schemes of Atheism and Irreligion' as well as 'Idolatry' and 'Fatalists.' It is true that many notions assume the existence of an external world, so I suppose a person who feels no need of it himself can wipe out a sea of contrary opinions in the one stroke of declaring idealism.
Between the positions of Newton and Berkeley, David Hume was agnostic about the question of an external world:
As to those impressions, which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and ‘twill always be impossible to decide with certainty, whether they arise immediately from the object, or are produc’d by the creative power of the mind, or are deriv’d from the author of our being. Nor is such a question any way material to our present purpose. We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses.3Hume apparently didn't think it mattered whether our senses are connected to an external world, so long as they are consistent enough for us to learn from their patterns. This attitude still comes up among practicing scientists today who focus on constructing models to fit the data, without worrying whether the model describes external reality.
Thomas Reid was explicitly responding to both Berkeley and Hume when he wrote:
All reasoning must be from first principles; and for first principles no other reason can be given but this, that, by the constitution of our nature, we are under a necessity of assenting to them. […] reason can neither make nor destroy them; nor can it do any thing without them: it is like a telescope, which may help a man to see farther, who has eyes; but without eyes, a telescope shews nothing at all.4He went on to draw an analogy from the way a mathematician must assume axioms, to the way a historian or witness must assume some trust for memory and senses, and to the way a natural philosopher (i.e. a scientist) must assume 'that the course of nature is steady and uniform.'
Gauch then spends a couple of pages discussing Immanuel Kant's contribution to the ongoing debate, but I'm having a really hard time understanding it even after reading other articles and excerpts. Apparently he thought space and time weren't part of external reality, but instead are the subjective medium upon which our sense experience is arranged. Or something. According to Gauch:
Such thinking was the beginning of constructivist or anti-realist views of science, that truth is constructed by us rather than discovered about nature.5A quick overview of the logical empiricism (or logical positivism) movement of the early 20th century closes out this chapter. My short version of his short version is that the logical empiricists tried to restrict meaningful language to whatever could be empirically observed or logically concluded, hence the name. Sounds reasonable at first, but since this precludes any sort of metaphysical presuppositions — like there being an external world that we're experiencing — it became very detached from common sense.
4. Reid, T. (2000). An inquiry into the human mind on the principles of common sense. (D. R. Brookes, Ed.) Edinburgh, Scotland: Edinburgh University Press Ltd. (Original work published 1764). p. 71
5. Gauch, H. G., Jr. (2006). Scientific method in practice. Cambridge: Cambridge University Press. p. 67