“If I concentrate hard enough on why I believe there is a tree in the Quad, I cease to assume that there is a tree in the Quad, and treat that statement instead as a proposition to be proved rather than a premise that is given. In having the question of whether there is a tree in the Quad or not brought to my notice I am being begged not to beg the question, and the courtesies of argument demand that I put in doubt what I normally know to be true. There is also what I might call the Yellow-Spot phenomenon in philosophy, namely, that if we focus our attention too hard on any matter for too long, we cease to see it straight. In the dark night of the intellect, which is the philosopher’s usual state of mind, it is wise for him occasionally to distract his thoughts and look away, that he may see what he is looking at the better; more especially when he is dealing with facts and certainty. For facts are essentially what is peripheral to the question under examination, what can be taken for granted on this occasion; and therefore by being asked sufficiently earnestly to consider any question sufficiently closely I can be cajoled into giving up fact-status for this occasion for almost any statement: courtesy compels. Only if I am making the minimum possible statement can I be pushed no further: only if I say that there is in my visual field at this moment a red rectangular patch on a cream background, am I safe from possible error: hence, if there are basic facts, only the simplest facts of sense-experience can fill the bill. By attempting to make rigid and absolute the flexible standard, which depends on the circumstances, of what the honest man cannot reasonably refuse to concede, we have ensnared ourselves in a reductionist spiral, demanding an ever lower standard of reasonableness until we reach the phenomenalist’s goal, the lowest common denominator of what must be conceded by every reasonable man in any circumstances whatever, that is, what must be conceded by a barely sentient being.
.....It is an interesting way of doing philosophy. We start by assuming that a fact is what a true statement states: from this it is a natural inference that since the conclusions of ethical debate and scientific theorising are not facts, they are not true either. By restricting our criterion of truth to that of agreed truth, we are able to eliminate all doubt and dubiety within the province of philosophy; nor can the opponent of this view fault the examples given of what is to be allowed as really true, for only those truths that cannot reasonably be contested are put forward as examples. One weakness alone attaches to the method: as there are few facts, if any, that we cannot in our metaphysical moments be uncertain of, our concept of truth is regressive; our criterion grows progressively and indefinitely more stringent. At first we exclude those propositions of morals, theology and metaphysics, whose elimination is welcome to many of the enlightened; but the more we think, the more nice we become as to what are unquestionable truths; and so the truths of logic, mathematics, and natural science, of common sense and everyday life, join the procession to the guillotine.”
J.R. Lucas, “On Not Worshipping Facts”, The Philosophical Quarterly, 8, 1958, pp.155-6, online at J.R. Lucas’s website.