SL: Interrelated Concepts, Methods, and Procedures:

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Logic texts are famous for pre-planning, pre-canning, and in general, formulating problems in logic that are almost perfect in every respect in terms of the way they work and what to do with them. When looking at a section of a logic text on testing arguments for validity, that is all you are required to do, and the concepts of consistency and inconsistency are usually ignored. But if you think that it is really that simple, then you are not attending to the concepts themselves, but are simply applying methods and principles blindly, without necessarily understanding the underlying principles behind those methods.

It seems unlikely that there is anyone who could truthfully say that he had never been presented with a group of sentences from which he is expected to formulate his own conclusion. When another person presents such statements to you and tells you to "make your own inferences", "form your own conclusions", or "see what you think", it is usually the case that what is intended is that you form a conclusion, i.e., complete the argument, for yourself. If you conclude something that does not follow from the premises, that is not the fault of the person who gave you the information, it is your own. YOU are the one who formulated the conclusion, and if the argument turns out to be invalid, it is your own fault. No set of premises (reasons) is ever valid or invalid, they are only either consistent or inconsistent. Whatever the case may be, the argument that you formulate, i.e., the conclusion that you present, is either consistent with the premises or it is not. But it is also the case that the person who gives you information has presented premises of a potential argument that are either consistent or inconsistent with each other. What you do with those premises is up to you.

If you know that someone has given you inconsistent premises (those that cannot all be true at the same time), then you also know that any conclusion you formulate will produce a valid argument. But you can also be sure that the argument that you form from those premises is not a sound one since inconsistent premises can never all be true, and the essence of soundness is validity AND truth, not validity alone. So if someone presents inconsistent information, you can disregard any conclusion that you might be tempted to draw from those premises when you are concerned not just with validity, but with truth as well.

But if someone presents to you a set of consistent premises, the conclusion you formulate must follow from those premises and the reasoning that you use to formulate it must be tight. If not, you will formulate an invalid argument by adding a conclusion whose falsehood is consistent with the truth of the premises. If you do that, the original information-giver is, again, not at fault. The point of logic is not simply to test other arguments (ones that other people present), but also to be sure that the arguments you formulate from information that you are given is arranged in a manner such that the conclusions you draw produce valid arguments. It is impossible to have soundness without validity, so the order of the day is validity first.

If you know that information that you possess is true and consistent, then you know that it is possible to formulate a valid argument from the statements used to present that information. But whether you formulate a valid argument from them is another question entirely. To draw a conclusion that follows from the premises, and which cannot possibly be false while all the premises are true is the essence of validity. To do this, you could guess, but in doing so, you might draw a conclusion that does not follow with necessity from the premises. But if you use already established rules of inference in the formulation of the conclusion (and use them correctly), the argument you produce is not only valid, but given true premises, must be sound as well. When you do not have a conclusion already pre-established, then, knowledge of the consistency of the premises is essential when your concern is also truth.

When someone tries to convince you that something is true, an argument is present. When an argument is present, there must also be at least one premise and a conclusion. In such a case, it might be beneficial to know whether the argument is valid or invalid, but that, alone, will not tell you whether the argument is sound. Thus, it might be good to know whether the premises that comprise the basis of the argument are consistent or inconsistent with each other. Again, you will know that the argument in question is valid when the premises are inconsistent, but you know something more important as well. You will know that the argument could not possibly be sound. But if you test the premises of an argument and find that they are consistent, it is possible that the argument is invalid. Thus, you must determine whether the argument is valid. If the premises are consistent with each other, and the falsehood of the conclusion is inconsistent with the truth of the premises AND you know that all the premises are true (which logic, in fact, cannot tell you unless the premises are tautologous), then you have a sound argument.

Unless you understand complex argumentation intuitively, it is probably not likely that you will simply know that an argument is valid without testing it in some way. And it is only in a textbook that you will know, prior to looking at the argument, that it is valid or invalid, or whether it has consistent or inconsistent premises.

You may never, outside of a logic class, do a proof of validity again. But the method and the principles will stay with you nonetheless, and it is an understanding of the interrelatedness of those methods and principles that is essential to an understanding of argumentation, and not just that which is valid, but that which is sound as well.