Philosophy 7 - 1.2.2 Logic

One of the first and most reliable ways that philosophers have of verifying and analyzing claims is by using logic, which is, in some sense, the science of reasoning. Logic attempts to formalize the process that we use or ought to use when we provide reasons for some claims. By interpreting the claims we make using logic, we can assess whether those claims are well founded and consistent or whether they are poorly reasoned. The chapter on logic and reasoning will provide much more detail about the nature of logic and how it is used by philosophers to arrive at truth.


The chapter on logic and reasoning covers this topic of logic in greater detail.


The first and most important move in logic is to recognize that claims are the product of arguments. In particular, a claim is just the conclusion of a series of sentences, where the preceding sentences (called premises) provide evidence for the conclusion. In logic, an argument is just a way of formalizing reasons to support a claim, where the claim is the conclusion and the reasons given are the premises. In normal conversation and even philosophical writing, arguments are rarely written so clearly that one can easily identify the premises and the conclusion. Nevertheless, it is possible to reconstruct any argument as a series of sentences with clearly identified premises and conclusions. This process is the first step in analyzing an argument: identify the claim that is being made, then identify the sentences that provide supporting evidence for the argument. This process will necessarily require some interpretation on the part of the reader. Therefore, it is important to try to remain faithful to the original intention of the argument and outline the premises and conclusions in such a way that they display the reasoning of the person making that claim.

Once the premises and conclusion are identified and written in order, it is possible to use formal techniques to evaluate the argument. Formal techniques will be covered in the chapter on logic and reasoning. For now, it is sufficient to note that there is a process for evaluating whether claims are well supported by using the techniques of logic. Poorly supported claims may be true, but without good reasons to accept those claims, a person’s support of them is irrational. In philosophy, we want to understand and evaluate the reasons for a claim. Just as a house that is built without a solid foundation will rapidly deteriorate and eventually fall, the philosopher who accepts claims without good reasons is likely to hold a system of beliefs that will crumble.


While arguments can be thought of as building blocks to construct a solid foundation for beliefs about the world, arguments can also be understood as explanations for phenomena that are evident but not well understood. To generate well-founded beliefs, we start with evidence in the form of premises and infer a conclusion from that evidence. To explain observed phenomena, we start with a conclusion in the form of some observation and reason backward to the evidence that explains why the observation is true. For example, we infer that there is a fire based on the appearance of smoke, or we infer lightning when we hear thunder, even if we do not see the lightning. We can compare the way we reason about explanations to the way a detective might reconstruct a crime based on the evidence found at a crime scene. By reconstructing the premises that led to a given conclusion, a philosopher can explain the reasons for a conclusion that are evident through observation. In summary, logical reconstruction can be used to investigate the world around us, providing a rational explanation for why the world is the way it appears.


Finally, logic provides philosophers with a powerful technique for assessing a set of claims or beliefs. We can ask whether a set of beliefs is logically consistent with one another. Given that we expect our beliefs to present to us a world that makes rational sense, we want those beliefs to be internally consistent. A set of beliefs or statements is coherent, or logically consistent, if it is possible for them to all be true at the same time. If it is not possible for statements or beliefs to be true at the same time, then they are contradictory. It seems unreasonable for a person to accept contradictory claims because a contradiction is a logical impossibility. If a person holds contradictory beliefs, then they must be wrong about at least some of their beliefs. Metaphorically, the house of beliefs in which they live must be poorly founded, at least in some places. When you are reading philosophy, you should be aware of places where the author says things that appear to be inconsistent. If you discover inconsistencies, that is a good indication that at least one of their claims is false. You may not know which claim is false, but you can know it is logically impossible for all claims to be true.

When faced with the possibility of incoherent beliefs, the philosopher will need to either revise those beliefs so that they become consistent, or they will need to give up some beliefs to preserve others. Logical consistency cannot tell us that a set of beliefs is true; a complete fiction might be logically consistent. But logical consistency can tell us what is not true. It is impossible for a logically inconsistent set of beliefs to be wholly true.

The content of this course has been taken from the free Philosophy textbook by Openstax