In this short lesson, part of the Legal Fundamentals Explained (LFE) series, Sara Azevedo (University of Lisbon) introduces the a contrario argument, a method of legal interpretation, explaining its structure and relevance in legal reasoning.
Below, you can find the full transcription corresponding to this video lesson*.
Sara Azevedo
Hello everyone. I’m Sara Azevedo, and today I’ll be presenting a brief introduction to the a contrario argument.
Here’s a quick overview of our plan for today. First, we’ll look at an example of the a contrario argument. Then we’ll explore two accounts of its nature. Next, we will discuss biconditionality, a key concept for both perspectives. And we’ll wrap up with some key takeaways.
Moving on to our example: imagine a norm stating that if you have a dog, you cannot enter a restaurant. Formally, this is expressed as: “If P, then it is prohibited to Q.”
Now, we can ask: what about cats? What about people without dogs? Does the absence of a dog a contrario imply that the person is allowed to enter, or can we only conclude that this action is not regulated by the law?
As I said, there are two ways of looking at the a contrario argument.
According to one view, the a contrario argument is interpretative in the sense that it justifies the semantic content of a normative statement in relation to the case at hand.
However, there is another way to look at the a contrario argument: it can be seen as a purely logical inference that only takes place after interpretation.
Let’s take a closer look at the interpretative account.
Under this account, the a contrario argument can be used to assert that the law was only meant to apply within its literal meaning, with anything outside of that being excluded. Consequently, a legal gap – or “illegal gap” – is identified, and it can be filled through analogy.
According to a different way of employing these arguments, the argument can be used to flesh out an implicit norm within the normative statement. In this case, there is no gap, because a norm was extracted from the normative statement.
Let’s unpack this by returning to our example.
According to the literal interpretation account – the one that connects the a contrario argument with literal interpretation – if the law only mentions dogs, then it does not regulate entering a restaurant with a cat, and we have a legal gap.
However, according to the creative interpretation account – the one that connects the a contrario argument with creative interpretation – if the law only mentions dogs, then entering with a cat is permitted. This is the implicit norm that has been extracted.
Focusing on this latter account, we must ask: how can we derive a permission to enter restaurants from a prohibition of entering restaurants with dogs? Is this logically correct?
No, it isn’t.
We cannot logically derive a permission to enter restaurants with cats from the prohibition of entering restaurants with dogs. In order for this to work, we need to add a second premise. This second premise basically says that when we have a text that states, “If P, then it is prohibited to enter restaurants,” this text should be interpreted as, “If and only if P, then it is prohibited to enter restaurants.”
Through this second premise, we can derive that when we have a cat or no animal at all, there is a permission to enter restaurants.
However, we can ask: where does this second premise come from?
Typically, it is said that it comes from other inferences. It is the conclusion of other inferences that rely on legal norms or practical principles of communication.
Let’s now turn to the logical account.
According to this account, the a contrario argument is not interpretative, because it does not help us to find the meaning of the words used in a normative statement. Instead, it is an inference drawn after interpretation is complete.
For the same reason, the argument is not creative. It does not create a norm; it simply draws logical consequences from a pre-existing norm.
And here’s the catch: this logical inference only works when the norm has a biconditional structure.
So, obviously, we need to understand what we mean by a biconditional structure.
A norm has a biconditional structure when the conditions required for its application are necessary, rather than merely sufficient – meaning that they are the only conditions that trigger the consequence.
In our case, being accompanied by a dog is the only condition that triggers the consequence of being prohibited from entering restaurants. Which is why we can logically infer that it is permitted to enter with a cat, or with no animal at all.
How can we tell if a norm has a biconditional structure?
Through interpretation – by looking at a normative statement and searching for expressions such as solely, only, exclusively if, and only if. These are all good indicators.
We can also look at other normative statements and other legal norms that are relevant to the case at hand.
To wrap up, we can say that the nature of the a contrario argument is a matter of debate. Some see it as an interpretative argument that allows for either the creation of a norm or the detection of a legal gap, while others view it as having a narrower scope, merely stating a logical inference.
According to the first view, determining whether a normative statement follows a conditional structure is part of the a contrario argument.
In contrast, the second view holds that identifying biconditionality falls outside the scope of the argument.
For both the interpretative and the logical accounts, biconditionality is a key issue – even though it is really difficult to spot. Besides that, as it is a conclusion reached by interpretation, it can always be open to debate, at least to some extent.
And finally, this is also why, contrary to popular belief, the conditions for engaging in a contrario reasoning are difficult to meet.
If you want to dive deeper into the topic, here are some great resources that you can check out.
Thanks so much for your time. You can reach me by email if you have any questions.
(*some minor grammatical and changes have been introduced in order to make the reading more fluid, but in no way altering the content or the format of each speaker’s interventions).
The LFE video series is powered by the EU Horizon Twinning project “Advancing Cooperation on The Foundations of Law – ALF” (project no. 101079177). This project is financed by the European Union.
