A proposition is the basic unit of any argument. It is a claim that is shown to be either true or false through the use of evidence and examples. In its simplest form, a proposition is the claim that “X is Y.” That: “Grammar is important for improving your language skills”; that “diplomacy is always preferable to war”; that “rugby union is better than rugby league”; that “Twilight is a travesty of literature!” Each of these is a claim: the subject (the words or phrase before “is”) is governed by the predicate (the words or phrase after “is”). The predicate governs the subject – the predicate is a fact about the subject that you are trying to prove. It governs the subject because the subject is to be understood in terms of the predicate.

But simply making the claim does not make the claim true – you need to support the proposition with relevant evidence.

“Twilight is a travesty of literature because it is poorly written and trashes centuries of accepted mythology that underpins much of the gothic or supernatural genre in the Western literary tradition. Vampires, for instance, are undead and cannot have babies; furthermore, vampires certainly do not sparkle!”

This is an argument; it makes a claim and provides supporting evidence. Is it true? Is it false? Is there a counterargument? Are there implications, or unintended consequences, to making this argument?

Notice the simple use of “is” (the copula) and “because” (a subordinating conjunction). The “is/because” structure is the simplest form of argument; no doubt, you use it every day in conversation with family and friends! Even the wonderfully circular argument: “It is, because I said so!” This is usually the argument of the older sibling who is sitting on your chest, pinning your hands to the ground! It is an argument – but it’s not a very good one.

A proposition in an argument is the point you are trying to prove – but you will need to use other propositions to prove it! These propositions are often called “premises.” In logic, a premise is a proposition that is accepted as fact. The premise for the argument “It is, because I said so” is that “I (the speaker and older sibling currently pinning you to the ground) have the authority to make such a claim and that by virtue of my authority the claim is true.” Again, not a strong argument.

In the Twilight argument, the premises are more subtle. The first premise is that “deviation from accepted mythology constitutes a travesty of literature”; this is a debatable point. The second premise is that “vampires can’t have babies because they are undead.” This is also debatable because the category of “undead things” is a fiction and is largely governed by usage (if you want undead things to breed in your story, you can just write that in – it isn’t a violation of physics or biology because undead things don’t exist!). Both premises are grounded in an appeal to convention: things have always been this way, changing them is just wrong! It is, nonetheless, a fact that vampires do not sparkle!

You will notice a couple of things about the structure of the simple proposition. The most obvious (because I’ve made it obvious) is the use of the copula: “is.” There are other variations to the copula, revolving around tense and number. In the simple proposition the copula acts like an “equals” sign, indicating that the subject is governed by the predicate; that the predicate is a fact about the subject, which you intend to prove.

You will also notice the use of the subordinating conjunction “because.” Together, “is” and “because” provide a simple structure: “X is Y because Z.” Most sentences will not (and should not) look like this; the general structure of your argument, however, should conform to this structure. The “is” is the proposition, or set of propositions, that you intend to prove, and the “because” is the evidence, analysis, and examples you will employ to prove it.

Generally speaking then, the copula, and the larger category of copulative, or linking, verbs, is essential to making an argument, as are subordinating conjunctions. Another category of words is also important: modal auxiliary verbs, or just modal verbs. Modal verbs express possibility or contingency. Sometimes, the choice is not between “is” or “is not,” but between “might” and “might not.” “Should” and “will” are also modal auxiliary verbs. “English can be difficult to learn” expresses the contingent fact that, for some English “is” difficult to learn, but that for others English “is not” difficult to learn.

A proposition that is characterised by a modal verb, and not a copulative verb, is called a modal proposition. For example: “English can be difficult to learn if you don’t have a good teacher.” “Can be” is a modal verb, while “if” is a subordinating conjunction. This can be converted into a hypothetical proposition: “If you don’t have a good teacher then learning English can be difficult.” A hypothetical proposition is an “if/then” argument; many “is/because” statements can be inverted to form a hypothetical proposition. This kind of conversion can help you analyse your own premises or the premises of a text you are trying to understand.

Here is another example of a modal proposition: “You should not read Twilight if you want a decent understanding of literature.” Or perhaps: “Reading Twilight can be detrimental to your intelligence.” The second proposition can be used in support of the first. The first is a special kind of modal proposition, however, as it expresses more than just a possibility. It is an imperative statement: it is expresses a command. Put another way, it expresses a course of behaviour you should undertake if you want a particular outcome, in this case “a decent understanding of literature.”

Supporting arguments must be employed in order to “prove” the claim. The second proposition can be used in support of the first: “You should not read Twilight if you want a decent understanding of literature; it can be detrimental to your intelligence.” But you will notice that the second proposition, or premise, is predicated on a modal verb: “can be.” The appropriate question to ask, then, is: “in what way can it be?”

It is important to note that, in any modal proposition there is an implicit acknowledgement that what is being claimed is not incontrovertibly true. If something “can be” it also “might not be.” Twilight can be detrimental to your intelligence because it is poorly written (to high literary standards) and it trashes an entire genre, but it is also popular and encourages people to read who might not otherwise pick up a book; it could also be a gateway to further reading (perhaps reading some proper vampire stories!).