Assumptions
Recall the two fundamental parts of an argument:
- That which is assumed to be true or its premises, which we likened to raw materials in a factory-line or the pillars of a building.
- A truth that is derived from part 1, which we call a conclusion and likened to a product that is developed from raw materials or the floors and ceilings of a building.
There is a third-part that is equally fundamental, but in the same way that it was unstated in previous lessons, it is most interesting because it is typically unstated: the assumption.
An assumption is an unstated premise. It can be said that it is a “missing piece” that is used to derive a conclusion.
As usual, we will demonstrate using our favorite example:
- I heard barking.
- There must be a dog. (1)
The argument is leading us from “I heard barking” to “there must be a dog”. Is there a missing piece or a gap between the support and the conclusion drawn?
In other words, is it the case that the sound of barking is enough to infer the presence of a dog? What if the sound came from a YouTube video or perhaps a very good imitator (or any other possibility)?
Consider that if someone made this argument, they would likely defend it by saying something like, “Look, if there is barking, there must be a dog!” They might even be irritated that we asked them to clarify their steps of reasoning. “How do you not see this? It is so obvious!”. It is often the case that assumptions may go unchecked because they are so obvious that they are easy to overlook or take for granted.
And sure enough, that “if there is barking, there must be a dog” is precisely the unstated premise that was left out of the example argument. With this assumption in place, the other possibilities are ruled out, because “if there is barking, then there must be a dog” tells us that the mere sound of barking always implies the presence of a dog.
Generally speaking, whenever an argument is not airtight, an assumption it has made is “if [whatever was provided], then [whatever was concluded]”. So, the quickest way to undermine such arguments is to imagine a scenario where whatever was provided is nonethless provided but an entirely different conclusion can be drawn. By so doing, you are showing that what was provided is not sufficient to conclude what was concluded, and so, the argument is missing a step and relying on an assumption.
- I heard barking.
- Maybe it is from a YouTube video or a very good imitator. (1)
If you ever come across such an argument, “I heard barking, so, there must be a dog”, you can respond with, “You are assuming that if there is barking, there must be a dog, an assumption that rules out the possibility that the sound came from alternative source, like a video or a good imitator, like that guy from Police Academy. You, my friend, need to trace your steps of reasoning a little more carefully.” Then, hope that you do not get chased or slobbered on by a hundred-pound German Shepherd.
Using the product analogy, the conclusion is supposed to be a product derived from the given materials. If it is missing a piece, the product is faulty. Similarly, if an argument relies on an unstated premise, it is an invalid argument. We will explore argument validity next.
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Enhance your critical thinking skills with Symbols Logic. Unlock access to
the first studycard and the first level of all activities for free. Get the
app now:
Recall the two fundamental parts of an argument:
- That which is assumed to be true or its premises, which we likened to raw materials in a factory-line or the pillars of a building.
- A truth that is derived from part 1, which we call a conclusion and likened to a product that is developed from raw materials or the floors and ceilings of a building.
There is a third-part that is equally fundamental, but in the same way that it was unstated in previous lessons, it is most interesting because it is typically unstated: the assumption.
An assumption is an unstated premise. It can be said that it is a “missing piece” that is used to derive a conclusion.
As usual, we will demonstrate using our favorite example:
- I heard barking.
- There must be a dog. (1)
The argument is leading us from “I heard barking” to “there must be a dog”. Is there a missing piece or a gap between the support and the conclusion drawn?
In other words, is it the case that the sound of barking is enough to infer the presence of a dog? What if the sound came from a YouTube video or perhaps a very good imitator (or any other possibility)?
Consider that if someone made this argument, they would likely defend it by saying something like, “Look, if there is barking, there must be a dog!” They might even be irritated that we asked them to clarify their steps of reasoning. “How do you not see this? It is so obvious!”. It is often the case that assumptions may go unchecked because they are so obvious that they are easy to overlook or take for granted.
And sure enough, that “if there is barking, there must be a dog” is precisely the unstated premise that was left out of the example argument. With this assumption in place, the other possibilities are ruled out, because “if there is barking, then there must be a dog” tells us that the mere sound of barking always implies the presence of a dog.
Generally speaking, whenever an argument is not airtight, an assumption it has made is “if [whatever was provided], then [whatever was concluded]”. So, the quickest way to undermine such arguments is to imagine a scenario where whatever was provided is nonethless provided but an entirely different conclusion can be drawn. By so doing, you are showing that what was provided is not sufficient to conclude what was concluded, and so, the argument is missing a step and relying on an assumption.
- I heard barking.
- Maybe it is from a YouTube video or a very good imitator. (1)
If you ever come across such an argument, “I heard barking, so, there must be a dog”, you can respond with, “You are assuming that if there is barking, there must be a dog, an assumption that rules out the possibility that the sound came from alternative source, like a video or a good imitator, like that guy from Police Academy. You, my friend, need to trace your steps of reasoning a little more carefully.” Then, hope that you do not get chased or slobbered on by a hundred-pound German Shepherd.
Using the product analogy, the conclusion is supposed to be a product derived from the given materials. If it is missing a piece, the product is faulty. Similarly, if an argument relies on an unstated premise, it is an invalid argument. We will explore argument validity next.
Want an interactive way to learn logic?
Enhance your critical thinking skills with Symbols Logic. Unlock access to the first studycard and the first level of all activities for free. Get the app now: