Unit Overview

In this first week, begin our study of moral philosophy with an introduction the basic conception of what it means to talk about moral issues from a philosophical perspective. Philosophers since the time of Socrates have focused attempting to figure out the rational principles that underlie moral reasoning. The reading for this week is taken from the first chapter from James Rachels’ textbook on morality. Rachels offers three case studies for our consideration and asks us to consider what we think is right in those cases. He concludes that the minimum conception of morality is “the effort to guide one’s conduct by reason.” This idea is one we will explore further as the course goes on.

We also get a brief introduction to the basics of logic and argument as these are the foundation of what we are doing in this course.


Logic and Argument:

Types of arguments

There are three basic types of arguments: deductive, inductive, and abductive, also known as “inference to the best explanation or “IBE”. All three types of arguments are merely formalizations of the types of reasoning we all use everyday completely naturally and unreflexively. While inductive and abductive arguments are formalizations of reasoning that we use everyday, deductive arguments are the very structure of thought. Ludwig Wittgenstein, author of the famous “Tractatus Logico Philosophicus” or treatise on logic and philosophy, notes that it is impossible to think “illogically.” He puts illogically in quotations marks because we really don’t know what that would mean and truthfully are not even saying something coherent when speaking about something that we might want to consider outside the domain of logic. Being familiar with various types of arguments can help us, when reading various arguments, to clarify the exact argument being put forward. And once we have a clear version of the argument being put forward we can then and only then set ourselves to the task of evaluating the argument. And more generally the study of logic and philosophy can help us to reason better and think more clearly in all aspects of our life. We are all constantly being bombarded with information and improving our thinking skills can help us to better sort through and evaluate this information.

Deductive Arguments

There are two basic things to evaluate when we are evaluating a deductive argument: validity and soundness.

A valid deductive argument is truth preserving. Truth Preserving means that if the premises are true the conclusion is guaranteed to be true. The premises cannot be true and the conclusion false. They preserve the truth of the claims being made, which is helpful in that we can be confident in our conclusion if our argument is valid and the premises are true. A deductive argument is valid if it is in the correct logical form. Validity refers only to the logical form of the argument and has nothing to do with whether the premises or the conclusion are true. An argument can be valid but the conclusion can be false and an argument can be invalid but nevertheless have a true conclusion. An argument can be valid but have a false conclusion because one or more of the premises may be false. If one or more of the premises are false we say that the argument is not sound. Here is an example of a valid argument with a false conclusion:

  1. If I don’t do the readings for this class, then I will get a good grade.
  2. I won’t do the readings for this class.
  3. So, I’ll get a good grade.

This argument is valid, in the correct logical form, but unsound because one of the premises is false. A deductive argument is sound if all the premises are true. As you can probably guess the first premise in the above argument is false, and therefore the argument is unsound. So, if an argument is valid and sound we know for sure that the conclusion is true. This means that when evaluating an argument we need to check for validity and soundness and when constructing arguments we should make sure our arguments are valid and sound.

The above was an example of a valid argument with a false conclusion now here is an example of an invalid argument with a true conclusion:

  1. Roses are red.
  2. Violets are blue.
  3. So, thirty plus two is thirty-two.

The conclusion happens to be true but the “argument” does not guarantee the conclusion to be true because the conclusion does not actually follow from the premises. This argument is sound in that all the individual premises are true, taken on their own, and the conclusion is even true, but the conclusion doesn’t follow from the premises because the argument is not in the correct logical form. The difference between the first and second argument is that the first is in valid logical form but the conclusion is false because one of the premises is false and the second argument is not in valid logical from, despite the conclusion being true. The conclusion is a non sequitur, which is Latin for “does not follow” i.e. the conclusion does not follow from the premises.

A conclusion follows from the premises if the argument is in the correct logical form. Although intuitively “logical form” is a concept we understand it is nevertheless unclear what exactly logical form is. Following Wittgenstein, as he discusses this issues in his book Tractatus Logico Philosophicus (Treatise on Logic and Philosophy), we will define logical form as the structure that the world and our thoughts and mental representations share. We make use of this structure everyday in our language and thinking and this structure can be represented more formally in the language of logic. Since the time of Aristotle philosophers have made attempts develop intuitive logic into a more formal language, and in doing so have identified various fundamental logical structures, also known as logical operators. These logical operators can be combined to create logical formulas. The common forms of argument that we use everyday are based on one or more of these logical operators. We will now look at some of the common forms of argument that we make use of everyday and that we will need to be familiar with as we move forward in the course.

The most common form of argument that we will be using is called modus ponens. The central logical operator is this argument is called a conditional or an “if-then” statement. The argument looks like this:

  1. If P then Q.
  2. Therefore, Q.

As you can see the argument structure is represented using variables. The actual things that end up filling in the variables don’t matter to the validity of the argument. Just make sure you put your “P” in all the places that it should go and do the same with your “Q” as well. Here is an example of an argument is in modus ponens form:

  1. If it is raining out then there are clouds in the sky.
  2. It is raining outside.
  3. Therefore, there are clouds in the sky.

This argument is valid as it is in a correct logical form. And it is sound, both premises are true, so, we know that the conclusion is true. It may be helpful, in the beginning, when analyzing an argument to isolate and label all the different variables. Parentheses can be helpful to do this. If you are unsure if the above argument is actually in modus ponens form write it out like this:

  1. If P(it is raining out) then Q(there are clouds in the sky).
  2. P(It is raining outside).
  3. Therefore, Q(there are clouds in the sky).

And once it is labeled like that you just have to make sure all your Ps and Qs match up.

Closely related to modus ponens is another form of argument call modus tollens, which looks like this.

  1. If P then Q.
  2. Not-Q.
  3. Therefore, not-P.

This first premise is the same as in modus tollens but the second premises is a denial of Q and then the conclusion is a denial of P. And using our previous example of rain and clouds we get:

  1. If it is raining out then there are clouds in the sky.
  2. There are not clouds in the sky.
  3. Therefore, it is not raining.

This argument is valid as it is in a correct logical form. And it is sound, both premises are true, and so, we know that the conclusion is true.

There are two logical fallacies that are closely related to the modus ponens and modus tollens. The fallacy that corresponds to modus ponens is called “affirming the consequent” and looks like this:

  1. If P then Q.
  2. Therefore, P.

The valid form, modus ponens, is when the second premise is P and the invalid form, affirming the consequent, is when the second premise is Q. The name also gives it way because “consequent” refers to the second part of the conditional, the if-then statement. The first part of the conditional is called the “antecedent” and the second part is called the “consequent”. Another helpful hint is that “consequent” is etymologically related to “consequence”, and a consequence, or consequent, is what comes after something. Sticking with our “rain and clouds” examples we get the following:

  1. If it is raining out then there are clouds in the sky.
  2. There are clouds in the sky.
  3. Therefore, it is raining.

The example is helpful because intuitively we know this form is fallacious because we know that there can be clouds without rain, but that there cannot be rain without clouds.

The other invalid form is know as “denying the antecedent” and looks like this:

  1. If P then Q.
  2. Not-P.
  3. Therefore, not-Q.

In modus tollens the second premise is a denial of Q but in denying the antecedent the second premise is a denial of the antecedent. Again, the name gives it away. And here is our example version:

  1. If it is raining out then there are clouds in the sky.
  2. It is not raining.
  3. Therefore, there are not clouds in the sky.

And again the example is helpful because intuitively we know that just because it is not raining it does not mean there are no clouds in the sky. These are ways of reasoning that we already use but by making ourselves more aware of them and practicing them we can better be able to identify fallacious modes of reasoning in our own thinking and in the materials we will be reading.

Another important deductively valid logical structure is known as a “logically syllogism”. The logical syllogism dates back almost 2,500 years to Aristotle, the father of logic in the Western philosophical tradition. There are a number of different types of logical syllogisms, with different names. They all contain a major premise (the first premise), a minor premise (the second premise), and a conclusion. The following form is known as a “Syllogism in Barbara”:

  1. All A’s are B.
  2. C is an A.
  3. Therefore, C is a B.

The example that is often used is the following:

  1. All men are mortal.
  2. Socrates is a man.
  3. Therefore, Socrates is mortal.


Logical Fallacies

The two ways we have discussed thus far that an argument can go wrong are that it can be unsound, i.e. one of the premises can be false, or it can be invalid, i.e. it can be in the wrong form. In addition to being unsound or invalid there are other fallacies or mistakes one must avoid in crafting an argument. We will discuss two different fallacies: equivocation and begging the question.

Equivocation is when one uses the same word in different places in the argument with different meanings. An equivocation involves a switching, sometimes back and forth, between two meanings of a word. The following example may help:

  1. Man is the only rational animal.
  2. No woman is a man.
  3. Therefore, no woman is rational.

When we using a more precise word than man it becomes clear that the conclusion does not actually follow from the premises. “Man” is used differently is the first and second premise.  And when we fix the usage more precisely it becomes clear that the argument is unsound. If we substitute the biological species definition of man we get the following argument in which premise 2 is obviously false:

  1. Homo sapiens are the only rational animal.
  2. No woman is a homo sapien.
  3. Therefore, no woman is rational.

Or if we substitute the gender definition of man we get the following argument in which the first premise is obviously false:

  1. Male homo sapiens are the only rational animal.
  2. No woman is a male homo sapien.
  3. Therefore, no woman is rational.


As you can see definitions are very important when doing philosophy, which is why philosophers often times take great pains to very precisely define the terms in their arguments. The equivocation is obvious in the above example but in many cases it will not be so obvious.

The other logical fallacy we will be covering is called “begging the question” and is also sometimes called “circular reasoning.” “Begging the question” is a technical term in philosophy and should not be used casually without care as to its definition in philosophy i.e. you shouldn’t casually say “This begs the question  …” unless it really begs the question in the technical sense. In logical an argument begs the question when the conclusion is stated in some form or another or assumed in some way in one or more of the premises. We’ll spend a little bit of time on this fallacy as it can be a bit more tricky and is also a very important one because it comes up often.

As an example, imagine two friends arguing about the existence of God. One claims God exists and the other is not convinced. As evidence the theistic minded friend offers a quotation from the Bible. The non-believer questions why he should believe anything the Bible says and the first friend responds by saying that the Bible is a reliable source of knowledge because it is the word of God. This line of reasoning is problematic because the non-believer is not going to believe that God wrote the Bible because he doesn’t believe in the existence of God. The theists line of reasoning has begged the question. We can see this more clearly when we write it out formally like this:

  1. Because it is the word of God anything the Bible says is true.
  2. The Bible says God exists.
  3. So, God exists.

The argument is supposed to be proving the existence of God but it begs the question because it assumes the existence of God in the first premise.

Let’s consider another example, this time from the history of philosophy. Some philosophers have wondered whether there really is a physical world or an external world that exists outside of our experience. The problem, known as the problem of the external world, is that all we have access to is our experience of the world, so it is not clear that we actually know anything about the world beyond our experience. Put in more familiar terms “How do we know we are not in some kind of matrix like experience?” Suppose a normal person happens upon a philosopher in the throws of an external world skepticism episode and says to the philosopher, “Of course the external world exists, and the fact that we can see it proves that it exists.” Our unsuspecting friend has just begged the question. The original question was “Does the external world exist?”, so no amount of evidence from the external world is going to be useful in proving the existence of the external world. The very question calls into doubt our sensory experience so sensory experience cannot be used to prove the validity of sensory experience. The naïve question begging argument runs something like this:

  1. Any thing I can experience with my senses is real.
  2. I can experience the external world with my senses.
  3. So, the external world is real.

This argument is question begging because the very question is “How do I know that any thing I can experience with my senses is real.”

Our third example pertains to content of our course and involves abortion. Suppose Jane thinks that abortion is morally permissible and John thinks it is not morally permissible. John offers the following argument:

  1. It is always wrong to kill an innocent human being.
  2. A fetus is an innocent human being.
  3. Therefore, it is always wrong to kill a fetus.

This argument begs the question because the reason Jane thinks abortion is morally permissible is because she doesn’t think fetuses are persons, so by making this claim in his argument John is begging the question. He is essentially assuming what needs to be proven.

How might we avoid begging the question in this case? There are lots of ways but here is one example that avoids, at least directly, the begging the question:

  1. It is always wrong to kill an innocent human being.
  2. Any being that has human DNA is a human being.
  3. A fetus has human dna.
  4. So, a fetus is an innocent human being.
  5. So, it is always wrong to kill a fetus.

This argument, although far from being perfect allows us to key in more clearly on the premise that needs attention. In this case it is the second premise. This argument suggests a definition for human and then claims that fetuses meet that definition, and therefore it allows us to begin to focus on the important question in the debate. With this argument in hand the parties can at least begin a rational dialog on the issue rather than flatly disagreeing.

There are a number of other dubious methods of arguing, of which we’ll just discuss a few.

Straw man Argument – A straw man argument is when instead of arguing against the actual argument one sets up a “straw man”, which is an argument that looks similar to the original but different is some important way, and then attacks the straw man while claiming to have show the original argument unsound or invalid.

Ad Hominem – Rather than addressing the argument a person may resort to attacking the other person’s character in an attempt to discredit them, which is not a logically acceptable way of arguing. A person’s character shouldn’t matter to the truth or falsity of the argument they are making. When doing philosophy we just focus on the argument being presented and leave the character of the person making the argument out of the picture, as it is not relevant to their argument. If their depraved character has led them to make a terrible argument then show how terrible their argument is without attacking their character.

Arguing from authority – Appeals to authority, whether a particular person or religious tradition, are not acceptable methods of arguing in philosophy. Again we are concerned with arguments and not people’s opinions or character. If there is some authority that believes something then we might have an extra interest in hearing their argument but ultimately when doing philosophy we should be concerned with and make our final judgment based on their argument.

Example: Einstein believed in God, so God must exist.

Other Types of Arguments

Thus far we’ve been discussing deductive arguments and now we will turn our attention to two other kinds of arguments: inductive and abductive.

Inductive arguments are the type of arguments used in science. Inductive arguments are empirical arguments as they rely on information derived from the senses and draw conclusion based on our experiences. Inductive arguments differ from deductive in that no inductive argument is ever one hundred percent guaranteed the way a deductive argument is. Here are two examples of deductive arguments:

Example 1:

  1. The sun has risen every morning in recorded history.
  2. Therefore, the sun will rise tomorrow.

Example 2:

  1. Every swan I have ever seen is white.
  2. Therefore, all swans are white.

As you can see inductive arguments lead to conclusions that are either stronger or weaker depending on the evidence and sample size whereas deductive arguments lead to conclusions are either true or false based on the soundness and validity of the argument. However, it is very important to note that many deductive argument rely on an empirical premises, which may give us reason to doubt the conclusion if the argument is valid. Consider the previous example, the syllogism in Barbara, wherein we had a deductive argument where one of the premises was that “All men are mortal” which is an empirical claim. The valid form of the argument guarantees the conclusion to be true if the premises are true, but even when making a deductive argument we cannot fully guarantee the truth of the conclusion if any of the premises are based on inductive arguments.

A closely related type of argument is known as abductive arguments, also called inference to the best explanation (IBE). Abductive reasoning also plays an important role in scientific inquiry and any scientific facts are inferences to the best explanation. Previous to Galileo it was thought that the sun orbited the Earth, this was thought to be the best explanation of certain facts. However, this explanation didn’t properly explain the movement of the other planets so Galileo hypothesized that the Sun was the center of the universe and that all the planets orbited the Sun and not the earth. This type of thinking is also employed constantly in everyday life. Imagine you come home and you sandwich is gone from your refrigerator and you assume your roommate ate it as you know he was the only one home. The difference between abductive and inductive reasoning is that abduction is a best guess looking at the evidence whereas induction is an explanation based on repeated observation and testing. A doctor uses abductive reasoning to make a diagnosis of a patient in a clinical setting but uses inductive reasoning in developing and testing a new theory in the lab.

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