The German philosopher Carl G Hempel, in his beautiful and elegant treatise written in 1965, demonstrated that there were flaws in the long held scientific processes of inductive reasoning, generalization, and falsifiability of logic as it is commonly understood and practised.
The background of inductive reasoning: Hempel used raven as a central point of his argument against the long held pattern of scientific reasoning and he used the following example: Imagine that you had taken a long walk as a scientist and you happened to see a raven that you noted to be black, you might make your comment and say, ‘’I saw a black raven.’’ If sometimes after that you noticed a few more ravens that were black, you might say ‘’what a perfect coincidence, these other ravens are black too.’’ If time passed by and in your adventure you happened to see more ravens that were black, the chances are that you could say ‘’this is much more that coincidence’’ and with the instincts and natural practice of an observant scientist, you therefore form a hypothesis ‘’All ravens are black.’’
Demonstration of the limitation of inductive reasoning and scientific methods: The example stated above may look too simple but it brings to light the first line of scientific method commonly understood and practised. Hempel showed that the background of inductive reasoning and scientific method amounts to making observations and thereafter form an inductive hypothesis.
The next thing that comes naturally to the scientist is to carry out experiments to either confirm or reject the hypothesis which is where the problem usually occurs. In this particular case, carrying out experiments involves having to observe as many ravens as there can be and then confirming that they are all black.
In practice and principle, it is rather impossible to observe every raven out there. It is obvious that many ravens do not exist again and many ravens are yet to exist. Besides, is it not possible that there could be some ravens that one would not want to call ravens just because they are albino ravens? And there are some like that! How about the possibility that some ravens may be living in some places that are inaccessible such as other planets? All these constraints of experimental procedure show that there are limits of experimental procedure even if such procedure involves mere observation of the color of as many ravens as one could find around.
Nevertheless the constraints of experimental procedures and apparatus, scientists still feel justified if they say that the hypothesis seemed to be confirmed by every new observation of a black raven. If in the process of time, there were no red, white, green, or any other non-black ravens observed, the hypothesis that ‘’All ravens are black’’ becomes accepted and it will without any doubt assume the status of a natural law.
The basis of illogicality of conditional hypothesis: Where the hypothesis has been accepted as a natural law, our concern therefore shifts to knowing if it is logical to do so simply because the hypothesis ‘’All ravens are black’’ is conditional in a way. It is more like saying ‘’if a bird is a raven, then it is black’’ or ‘’if X then Y’’ in a general conditional statement form. With respect to the laws of logic, a conditional statement and its contrapositive are equivalent.
If we again consider the hypothesis that ‘’All ravens are black,’’ it implies by equivalence that ‘’all non-black birds or things are not ravens’’ so that if when we see every black raven confirms our hypothesis, then every non-black bird or thing we see should equally confirm the hypothesis. That is a form of illogicality since if I see my cloth and it is not black, I jump in confirmation that all ravens are black. But that has no end for I can continue with all manner of things that are blue, red, yellow, in fact everything that is non-black and therefore use that to strengthen the hypothesis further which is ridiculous and rather unacceptable.