When I was a young engineering student, I was very impressed by techniques that seemed to deliver something from nothing – or from surprisingly little. For example, one of Kepler’s insights was that orbiting planets “sweep out equal areas in equal times”. Newton later proved that this follows from nothing more than gravity acting along the line joining the centres of planet and Sun. The force’s magnitude needn’t be that of an “inverse square” law; it might even be repulsive instead of attractive – all that matters is that it act radially.
As another example, consider “dimensional analysis”. We might suppose that the period of a simple pendulum depends on variables such as its length, its mass, or acceleration due to gravity. But by simply noting that the period must be measured in units of time (rather than of mass or length, say), we can show that it must be proportional to the square root of the pendulum’s length divided by acceleration (i.e. the constant g). And it cannot depend on the mass of the bob. Here again, a modest assumption about a constraint yields a surprisingly powerful result.
Something rather like this can also happen in philosophy. Take the modest assumption that science posits entities that cannot be observed directly – such as electrons, viruses, force fields and dinosaurs. This constrains scientific methods in surprisingly powerful ways. For a start, it immediately puts the two traditional patterns of reasoning into the back seat. Scientific method cannot be much like mathematics, whose methods of proof are exclusively deductive. Nor can it be much like Francis Bacon imagined it to be in the late sixteenth century, as the rigorous application of induction.
Deduction cannot deliver nontrivial conclusions of valid arguments containing terms that do not appear in the premises. So any entity purportedly denoted in such a conclusion must already be denoted in the premises. Where do these premises come from? – Ultimately, they themselves cannot be the product of deduction alone.
Induction too can only deliver more general, extended versions of claims already made. So where do these original, less general claims come from? – Typically they are about things that can be observed directly. Those claims don’t even purport to describe things that can’t be observed directly. The few inductions that start off by purporting to describe such things cannot themselves be the deliverances of induction.
The problem with both deduction and induction is essentially the same: each starts off with some claims that are already accepted, but which describe nothing beyond what can be observed directly. Each then makes a sort of “jump” to a “new” claim, but nothing “new” enough to contain anything of the sort we’re interested in in science, namely a description of something that cannot be observed directly. Genuinely scientific “jumps” to what cannot be observed directly must be of a different sort from anything made in deduction or induction.
So science must – I repeat, must – be a matter of guesswork. Of course it must also be more than guesswork if it is to produce anything worth believing. That essential extra bit is testing.
There is a variety of takes on guesswork, each with its own fancy name. Some call it the “method of hypothesis”. Others call it “abduction”. Some like the sound of “inference to the best explanation”. And there are other words like these. But most of them are vague, and all are misleading inasmuch as they suggest that step-by-step reasoning is involved (analogous to traditional deduction and induction) instead of honest, common-or-garden, risky guesswork.
Most of those fancy words are inspired by discomfort or even hatred – hatred of uncertainty, of risk, of depending on luck, of gambling, of being unable to do anything remotely like accountancy. So people who hate those things tend to resist or even to cover up the fact that science is essentially guesswork.
One “radical” attempt to disguise the fact that science starts off with guesswork is to pretend that science does not in fact posit entities that cannot be observed directly. So they say instead that all our talk of electrons, viruses, force fields and dinosaurs is a mere instrument to “organize experience”. Scientific theories are neither true nor false, they say, but consists of mere “models” which we use to predict how the world as we experience it will unfold.
It’s a long, old debate – over the issue of scientific realism – and I’d be happy to join it with anyone who’s willing to take me on. In the meantime, please note that if we understand science in an instrumental way, it cannot challenge our religious or philosophical beliefs, or even earlier scientific beliefs. In fact it is powerless to do anything interesting at all.
There is a sort of trade-off in these opposed attitudes to science. The scientific realist accepts that scientific knowledge is very risky in that it cannot avoid guesswork, yet it presents a real challenge to other beliefs because it purports to be literally true. The scientific instrumentalist, on the other hand, sees scientific knowledge as more like accountancy – it is secure, but buys its security at the cost of being very shallow. It cannot present any real challenge to other beliefs because it can’t contradict them.