Thursday, 21 December 2017

The Raven Paradox

The scientific process is based on the condition of induction. For the uninitiated, this is a fancy term for 'observation' and any initial scientific hypothesis is always based on input from our senses. Consider the hypothesis: 'All Ravens are black'. After many observations of seeing only black ravens, let us say 2,000, it would be reasonable to accept the prior hypothesis. The more black ravens we encounter, the more our hypothesis stands firm and eventually moves from the status of hypothesis into the realm of 'law'. There are two points to be made here: One, it is impossible to sample all ravens, past and present. Most ravens that have existed are no more, and therefore beyond mortal tally. Other ravens remain beyond scrutiny due to their location in remote, or difficult to access geographic environments. The second point is self-evident. The observation of one non-black raven is all that is required to tumble our 'law' and destroy its scientific credibility. From a practical point, our hypothesis was never really on sound ground. Indeed, it is known that about 1 in 10,000 ravens are born albino. Very few of these mutant birds make it to adulthood as they are sickly and because of their lack of pigment, prone to predation. A dedicated bird watcher might spend a lifetime 'twitching' and not see a single albino Raven, and yet they exist.

This simple scenario undermines one of the great tenets of science- the notion of falsifcation. True scientists should not only be gathering data to reinforce their beloved theory but also, if he/she is scrupulously honest, be actively seeking evidence to undermine the theory. This, of course, is the counsel of perfection. The concept of 'falsification' was made famous due to the work of the great science commentator, Karl Popper. You can view my commentary on his propositions, hereThis simple mind game exposes a fundamental flaw in the design of the scientific method. Although the falsification of a hypothesis, or theory, is technically feasible, in practical terms, the necessary data may not be readily accessible.

The second part of the paradox is more interesting and instructive and concerns the deductive aspect of the scientific method. In logic when we posit: ‘All ravens are black’ we must accept the contrapositive statement: ‘Everything that is not black is not a raven’.  Seems fair enough, don’t you think? So, any non-black object is denied the possibility of being a raven- in logic this is irrefutable, given the original premise. Thus, any non-black object supports our hypothesis, even a green  apple. Surely the data set in this instance is bordering on the infinite and the trivial at the same time, but the underlying logical principle is sound. Here we illustrate a basic dichotomy between induction and deduction. In this instance, induction is responsible for our logical posit. But as we have seen previously, 'All ravens are black' is a false hypothesis and logic based on a falsehood will give an incorrect answer even though the logical process is impeccably valid.  

Does all this sophistry destroy the scientific method as a means of obtaining knowledge? Of course not, it would be stupid to propose or advance such a notion. The scientific method clearly works or our technological civilisation would and could not exist. Science must be getting something right. Remember, science does not give infallible knowledge and is bound by the principle of improvement.

The Raven paradox is a philosophical tool for the prudent scientist to apply in order to examine each step of the scientific inductive process with intellectual rigour. In many day to day scientific endeavours the raven's paradox will not apply. The paradox should not be viewed as a means to cripple science, but as a hobble, gently applied. A process to limit scientific hubris and to place the inductive method, with its limitations, within the canon of available knowledge. 


  1. I don't see a paradox here.

    You can never prove a null hypothesis (All ravens are black (because all that I have seen are black)). You can only accept it, with all the caveats that implies. But a single counter example disproves it.

  2. The paradox is about epistemology: it shows that inductive reasoning violates intuition. According to the paradox, the properties of objects can be confirmed by observing other objects which do not have these properties. That is the essence of the paradox. Admittedly it is more subtle than most and is not glaringly obvious. My particular interest is how we define and refine the concept of knowledge and knowledge base. What we call 'intuition' is often based on reason, if only we could articulate it. Have a great Christmas, Mark.

  3. No cat has eight tails. All cats have one tail. Therefore 1 cat plus no cat has 9 tails.Therefore all cats have nine tails. Ok Manxs' have a stub tail..