Conditionals and Modal Expressions
This article is going to start by covering the three main types of complex statements: conjunctions, disjunctions, and conditionals. You may remember from the last article that a conjunction is when two simple statements (conjuncts) are joined together with an ‘and’; for instance, “Stef produces podcasts and Stef produces videos”.
Disjunctions are another form of complex statement that consists of two simple statements joined together by an ‘or’. An example is “I am going out for dinner or I am going to the movies”. This seems very simple but ‘or’ is actually a tricky word. Believe it or not, it has two related but different meanings. When we use the word ‘or’ in natural language, we use it in one of two ways; inclusively or exclusively. Inclusive ‘or’ is when you are asserting that at least one of two statements is true. Exclusive ‘or’ is when you are asserting that exactly one of two statements is true. This may seem like a minor difference but it becomes crucial when dealing with arguments. If I said “when I get home from work ill watch tv or do some homework” I am typically saying that I will do at least one of those things, but I could still do both. If I stated “either he is old enough, or he isn’t old enough” I am saying that only one of the two simple statements is true, and it’s not the case that both are true. You will come across both types of ‘or’ when reading natural language. We call the simple statements in a disjunction the disjuncts.
The third type of complex statement we will be dealing with are conditionals. Conditionals are statements or sentences of the form ‘If A then B’, where A and B are statements. The two parts of a conditional are called the antecedent and consequent. A conditional is of the form ‘If [antecedent], then [consequent]‘. Conditionals are not arguments, they do not assert either A or B, they only assert the relationship between A and B. In the following example; “If Stef grows a mohawk, his ratings will increase” I am not asserting that Stef has grown a mohawk, or that his ratings have increased. The only thing I am asserting is that if the antecedent is the case, then the consequent is also the case. When dealing in natural language, again there is ambiguity. Conditionals can take different forms, sometimes there is no ‘then’ in the sentence, and sometimes the order of the antecedent and consequent will be reversed. The function rather than the form is what you must look for (that must be getting boring by now!)
There is a group of words and expressions that can be especially problematic when dealing with natural language and arguments, these are called modal expressions. Modal expressions are things like ‘necessarily’, ‘must’, ‘has to’, ‘must not’, ‘cannot’, ‘possibly’, ‘probably’, ‘may’ etc. These words and expressions are used in many different ways in natural language, and I will deal with a few of those here.
Modal expressions can be used to say something is necessarily true or necessarily false. To say something is a necessary truth is to say that is has to be true. Some examples are “2+2=4″,” a bachelor is an unmarried man”, and “you cannot be in two places at once”. These could not be any other way. These are in contrast with contingent truths, which are things that happen to be true, but did not have to be that way, such as “it is cloudy today”, “Stef has a daughter”, and “people in England speak English”. The same concept applied to necessary and contingent falsehoods.
A second way modal expressions are used is to make statements about capacity. Some examples of this type of use are “I must get a good night’s sleep to be alert tomorrow”, “she cannot run a marathon”, and “humans cannot fly”. You can see that these are expressing something different from necessary truths and falsehoods, but the same terms are used. The word ‘necessary’ is often used in natural language to mean something different from necessary truth. It is necessary to make the distinction to successfully interpret arguments (see!).
The third way that modal expressions are used is as inference indicators, which we covered in the last article. An example would be “that manuscript cannot be genuine, because it uses modern ink”. In this case, ‘cannot’ is being used to mean ‘is not’. It is not expressing a necessary truth or a capacity, it is simply acting as an inference indicator. Often it is not clear which function a modal expression is taking on in natural language, especially when someone is reasoning about capacities or necessity and contingency. These types of errors can lead to fallacies in philosophical reasoning because the same term can be used for different things. You can often find these types of issues coming up when discussing free will and determinism, so watch out!