According to our current understanding, humans have always attempted to expand and revise their knowledge, study, explore, and collect new experiences, and enlarge the realm of the known throughout history. This led to further inquiries on the nature of knowledge and the possibility of ensuring its accountability. Philosophers, scientists, and knowledge seekers have identified two methods for obtaining knowledge: induction and deduction. The two present strengths and weaknesses that make them indispensable for the cause but also potentially unreliable or inconclusive.
The Process of Obtaining Knowledge
All of us hold knowledge. For example, we know that if the sky is grey and cloudy, it will likely rain soon. A woolly jumper would warm us up, and a cotton T-shirt would cool us down. If today it is Monday, tomorrow it is Tuesday. An hour is equal to sixty minutes, and so on. As knowledge holders, however, we are bound to enquire where the information comes from and how we came to consider it true.
Philosophers and scientists who have considered and studied the problem of knowledge have identified two systems we repeatedly use to obtain and confirm our knowledge. These two systems are known in philosophy as Inductive Reasoning and Deductive Reasoning. The two have generated centuries of heated debates in Western Philosophy. Inductive Reasoning is considered indispensable for its second-to-none productivity, as it allows one to make infinite predictions. On the other hand, Deductive Reasoning is highly valued for its reliability. The process through which new predictions are generated makes them incredibly accountable.
Hence, many have questioned whether one is superior to the other. In the following paragraphs, we will expound on how their strengths and weaknesses might make it beneficial to consider them complementary.
An Overview of Inductive Reasoning
Inductive reasoning is the most creative and productive of the two systems identified for deriving knowledge. It is the method used in scientific fields. Inductive reasoning is the system at play when we develop a statement that generalizes it from numerous individual and independent observations about a phenomenon.
Imagine, for example, seeing some smoke. Walking closer to the smoke, you observe that its source seems to be fire. The following day, you see smoke again and repeat the operation by observing that its source is fire. You repeat the process every day for a month, concluding that every time one sees smoke, it must be generated by fire.
By reasoning this way, one has not observed all instances of smoke caused by fire in the universe. Hence, the claim that fire is the source of smoke is not supported solely by actual observation and empirical evidence but rather by the argument that there exists a connection between smoke and fire since, according to our observations, every time smoke has been seen, its source has been fire.
Therefore, inductive reasoning can be described as deriving a universal and generic claim about the universe from a series of particular independent observations about a phenomenon. It is crucial to note that nothing in the individual observations suggests a connection between the events observed (in our example, smoke and fire) other than that the two events have always been observed in co-occurrence. Therefore, statistics may suggest the likelihood of a connection between the events.
An Overview of Deductive Reasoning
Having expounded on the functioning of inductive reasoning, we can now consider deductive reasoning to be the opposite process. While also concerned with deriving knowledge, the process involved in such derivation follows the opposite train of thought. Owing its origin to Aristotelian Logic, deductive reasoning consists of using true premises—or premises whose truth value can be tested—to logically derive a true conclusion.
A practical illustration of the process would be the following, where (1) and (2) consist of the premises and (3) consists of the conclusion:
1) All humans are mortal.
2) Socrates is a human.
Hence
3) Socrates is mortal.
Once it has been established that premises (1) and (2) are true, the truth value of (3) follows logically. It cannot be denied without incurring the natural consequence of denying the truth of premises (1) and (2). Deductive proofs give us conclusions that ensure certainty, given that the premises are true.
Hence, deduction works in the opposite direction from induction. It involves taking generic and true premises that state something about the world and logically following from them a statement about a particular and unique phenomenon. Therefore, we could summarize the matter by saying that inductive reasoning operates from the particular (independent observations) to the general (universal claim). In contrast, deductive reasoning starts from general universal claims to logically derive particular information, working in the opposite direction.
The Problem of Induction
The derivation of knowledge through inductive and deductive reasoning is highly debated in philosophy. Both systems present limitations but are also indispensable tools for searching for knowledge.
The problems of inductive reasoning are very well-known and widely discussed among philosophers. The first formulation of what is known as The Problem of Induction is attributed to the Scottish philosopher David Hume, even if several others after him have attempted to find a solution to it and reiterated its validity. Hume was the first to argue that knowledge obtained through inductive reasoning is overall unreliable. A universal and general claim derived through induction—such as that smoke is generated by fire—is grounded on the existence of a connection between two events. However, nothing in the nature of two events, such as “smoke” and “fire,” suggests the existence of such a connection, and the claim that smoke is generated by fire is simply grounded on the fact that one’s observations have always reported it to be the case.
Hence, for how appealing inductive reasoning may seem, one must face the impossibility of proving the existence of the connections upon which induction relies. The fact that the presence of such connections cannot possibly be confirmed deems all the knowledge obtained through induction ultimately unreliable.
The Problem of Deduction
Similarly, deductive reasoning is also epistemically problematic. In the Critique of Pure Reason, Immanuel Kant argued that being satisfied with deductive reasoning for deriving epistemic knowledge could not be fruitful. He discusses the process of deduction while distinguishing analytic from synthetic judgments, where analytic judgment can be understood as judgments obtained through deduction. On this matter, he says that judgments obtained through deduction (analytic) can be defined as:
“judgments of clarification […] since through the predicate [they] do not add anything to the concept of the subject, but only break it up using analysis into its component concepts, which were already thought in it (though confusedly).”
Hence, deductive reasoning allows one to derive knowledge from verified premises through a process that does not generate new knowledge but derives new conclusions from already-held knowledge. Therefore, by relying exclusively on deductive reasoning, the knowledge one already holds can be further clarified; however, no new knowledge can ever be generated.
For example, when considering the following deduction:
1) All humans are mortal.
2) Socrates is a human.
Hence
3) Socrates is mortal.
The fact that Socrates is mortal is not a new piece of information obtained but rather a particular instance of the premises being spelled out and clarified. In other words, it is non-additive.
It follows that deductive reasoning, while able to guarantee more epistemic certainty about the knowledge it derives, remains insufficient as a theory of knowledge derivation. It is not productive or ampliative but simply clarifies the knowledge already held. Therefore, while deduction could play a role in ensuring the epistemic validity of certain knowledge and further clarifying it, it could not act as the sole means to obtain knowledge due to its lack of productivity.
Complementary Methods of Knowledge
While outlining the challenges that induction and deduction face, it becomes apparent that the strengths of each complement the faults of the other.
On the one hand, induction faces the objection of being epistemically unreliable. However, its productivity is second to none. Inductive reasoning allows one to derive new knowledge by finding connections between individual instances of empirical observations in a potentially infinite fashion. Thanks to the use of inductive reasoning, most of the scientific discoveries we have made throughout history have been possible. Hence, it is no surprise that the scientific method itself is grounded in inductive reasoning.
On the other hand, deductive reasoning faces an extreme lack of productivity in favor of an important, but not quite sufficient, clarificatory purpose of already held knowledge. However, it must be considered that all knowledge derived through deduction can enjoy a level of epistemic reliability that could never be attributed to any piece of information obtained through inductive reasoning. Deductions are instances of a general claim about the world already verified, of which a particular is simply spelled out. Hence, whatever is derived through this system is probably not new, but—unlike information obtained through induction—it is certain and reliable.
It follows that, while productivity is impossible without availing of inductive reasoning, ensured epistemic reliability would be lacking by dismissing deductive reasoning. Hence, attempting to derive all knowledge through one of the systems or trying to establish the superiority of one over the other is counterproductive for the quest. None of the two can be availed of as a unique source for deriving knowledge, but rather, only a collaborative effort of the two can efficiently support the requirements for accuracy and productivity that knowledge seekers hold.
