Last year I wrote two short articles about philosophical arguments – one about what they are and the other about how to evaluate them. This time, I look at two arguably best-known types of arguments and offer their brief introduction – deductive and inductive arguments. Both names refer to the structure of your argument, how it is built to illustrate your point.

In the last couple of days, I have been reading about the philosophy of knowledge and found out some interesting ideas put forward by various thinkers concerning the way in which humans can gain knowledge. Among these ideas, one surprised me and caught my attention by its simplicity and profoundness at the same time. In the 18th century, a Scottish Enlightenment philosopher David Hume presented an elegant and, in my view, still relevant challenge to the very foundation of the natural science’s method – induction. It is often referred to as Hume’s dilemma and it basically says that inductive arguments cannot be rationally justified. I intend to dedicate a separate article to this topic as I think it deserves additional attention. However, before that, it is necessary to do the introductions of the main ‘protagonists’ – deductive and inductive arguments.

Our first protagonist – deductive argument. This also sometimes called a valid deductive argument. The reason is that by its very nature, a deductive argument is structured in such a way that the truth of its premises necessarily transfers to its conclusion. The Ancient Greek philosopher Aristotle described deductive reasoning it in his works on logic and emphasised that from certain supposed things (premises) something (conclusion) results “of necessity”. In other words, a contracting conclusion simply cannot exist, it is inconceivable due to the logic of the deductive argument’s structure than ensures its conclusion’s validity.

A famous example of an argument that is deductive in structure:

Premise 1: All men are mortal.

Premise 2: Socrates is a man.

Conclusion: Socrates is mortal.

So, we can say that deductive arguments guarantee certainty and truth of their conclusions provided that their premises are true. The link that is built into its structure works. However, in its strength is also one of its weaknesses. The link does not work backwards. A true conclusion does not necessarily mean that all premises are true. For instance:

Premise 1: All mammals eat mice.

Premise 2: Cat is a mammal (or Cat eats mice).

Conclusion: Cat eats mice (or Cat is a mammal).

It still remains a valid argument and it has a true conclusion (either of 2 options) but it clearly has a flaw – premise 1 is simply not true. There are mammals who do not eat mice and there are some who are vegetarians. Therefore, to summarize, deductive arguments are by nature valid and they guarantee that the truth of the premises will be transferred to the conclusion making it true as well. However, this link does not work backwards and a true conclusion does not necessarily mean we have all our premisses true as well. Besides, it is very difficult to find such absolute general statements that are always true and use that as a basis for further learning. Some philosophers have suggested that deductive reasoning is more suitable for abstract areas of human knowledge, those that deal with ideas, not with something that exists in the natural world. Because to gain knowledge about the natural world, they argue, we cannot start from a general true maxim and go down to the particular details (deductive approach), we need to observe the particular phenomena, gather experience and based on that make conclusions about the general state of affairs (inductive approach).

Our second protagonist – inductive argument. As already briefly mentioned, this is a type of argument that is structured in a way of proceeding from a particular to the general. From something specific that we have experienced to our overall view that this experience will remain the same in the given circumstances.

We use inductive reasoning all the time in our everyday lives. I always take the bus at 08:00 near my house in the morning, it came at that time yesterday and the day before, so I know that it will come also today and tomorrow. It works also into the past. I eat bread and everyone I know eats bread, so people must have always used bread in their diets. The process of induction is basically learning from, relying on and giving authority to our experience. Nothing wrong with that. We just need to keep in mind that this type of reasoning does not guarantee the truth of its conclusions. Even if our premises are true, the conclusion can still be false. Since it is based on experience and experience is always limited (here’s one general true maxim for you 🙂 ) there is no link built into inductive arguments that would make their conclusions necessarily receive the truth from their premises. Contradicting outcomes are possible and they are easy to conceive. Just think about my example with bread. Even if my experience and that of people I know is true, it does not necessarily mean that people have always eaten bread in the past (or that everyone eats it now, for that matter).

Nevertheless, induction is at the heart of the empirical approach of many sciences and also we cannot do without it in our daily lives. It would be paralyzing never to trust my experience, absolutely counter-intuitive. Yet, induction has also very obvious drawbacks as presented here.

Perhaps there are solutions to the problem of induction. Some have been suggested. However, in one of my next articles, I would first like to present this problem in more detail. The problem by the intriguing name of “Hume’s dilemma”.

keep exploring!