What is the name of the fallacy: "If you buy XXX, which is expensive, then you would also buy YYY, because if you spent so much on XXX then you would spend as much on YYY."

The fallacy implies that both things should go together because both are expensive, and if one person has money for one, he also has money for the other.

For example, "You would never buy caviar if you don't also buy silver plates." It is false because a person may have just enough money to buy caviar, and want to know how it tastes, but if he also were to buy silver plates, he would not have enough money to taste the caviar.

  • I made some edits which you may roll back or continue editing. Welcome to Philosophy! Commented Jan 7, 2019 at 17:45
  • This just seems like the suppressed premise that these two things are equally desirable to everyone, and that purchases are independent. Excessive uniformity and presumed independence are very common suppressed premises. They are components of the Gambler's fallacy, but that is not the form they take here.
    – user9166
    Commented Jan 7, 2019 at 18:00
  • 3
    I had to re-learn some of how to manage money when I realized that I had enough money to get anything I wanted, but not enough to get everything I wanted. Commented Jan 7, 2019 at 22:58
  • This may not be a fallacy but perfectly true: 'I have a Victorian silver knife and fork, so I must get and will buy Victorian silver dessert and soup spoons to match'. Only, it is a bare psychological generalisation. Of whom it holds true, and in respect of what things, is impossible to say on the evidence given.
    – Geoffrey Thomas
    Commented Feb 6, 2019 at 19:50
  • There are quite a number of options ta consider, mon ami. Good luck!
    – Hudjefa
    Commented Jun 19, 2023 at 13:56

5 Answers 5


This seems to be a variation on "All horses are the same color". In other words, it is incorrect induction, where the base case is that you have already bought something expensive. The fallacy is in the inductive hypothesis that you will therefore buy another expensive thing, which does not necessarily follow (in contrast to correct induction, where we can show recursively that the hypothesis does hold in general).


Bo Bennett describes pseudo-logical fallacies as those which fail his test of being true fallacies. His test has three criteria:

  1. It must be an error in reasoning, not a factual error.
  2. It must be commonly applied to an argument either in the form of the argument or the interpretation of the argument.
  3. It must be deceptive in that it often fools the average adult.

Here is a description of the situation that may be a fallacy:

"If you buy XXX, which is expensive, then you would also buy YYY, because if you spent so much on XXX then you would spend as much on YYY."

This may be more of a factual error than an error in reasoning itself. Also it may not be commonly used in an argument nor deceptive. On the surface this does not appear to be fallacious.

That doesn't mean people haven't named something like this as a fallacy. In his page on what he considers pseudo-logical fallacies Bennett lists a couple named pseudo-fallacies that might fit this description:

Essentializing Fallacy: Suggesting that something is what it is and it will always be that way when in fact, that is not the case. This is simply factually incorrect.

Faulty Sign: Incorrectly assumes that one event or phenomenon is a reliable indicator or predictor of another event or phenomenon. This is very similar to many of the fallacies related to causality. This name is rarely used.

Bo Bennett, "Pseudo-Logical Fallacies" Logically Fallacious https://www.logicallyfallacious.com/tools/lp/Bo/LogicalFallacies/6/Pseudo-Logical-Fallacies


Faulty generalization. Sometimes also known as "hasty generalization."

The line of reasoning is that you are a person who spends money on expensive things. Certainly one piece of evidence is insufficient to establish that by inductive reasoning, and it neglects other possibilities, such as you spend very little on other things because you are so obsessed with XXX.


The problem is not some fallacy, the problem is that you made up a rule without any justification, and that rule is quite obviously false.

One reason that it is false is that it ignores the value of objects. You wouldn't buy an expensive item for ten times what it is worth.

The second reason it is false is that it ignores the subjective value of items. There are two expensive pictures that I could buy. Just because I buy the one I like, doesn't mean I will buy the other expensive one that I dislike, right?

The third reason it is false is that to buy more than one expensive item, you need more money. I may be able to buy expensive item A, or expensive item B, but not both.

The fourth reason it is false is that buying one expensive item can change the value of another expensive item. Two 70" TVs from two different manufacturers, both expensive. I might buy one because it gives me good value. The second one has zero value to me.

Now if you really want a fallacy, take the fallacy of "applying incorrect rules". If you start with an incorrect rule, like here, and apply it, your outcome will very likely be wrong.


A fallacy is a non-sequitur of a deductive argument. So first of all you'd need to formulate that in the respective form and then you'd search for where it goes wrong.

Also the important part is to realize that something is wrong and where it goes wrong and why not to give it a fancy name.

So in your case the underlying idea seems to be:

A is necessary for B

You do B

therefore you need to have A

Now that could be wrong for various reasons, like you could say "you need a spoon to eat soup", you want to eat soup therefore you need to have a spoon.

But while that is how you usually eat soup you could also eat it with a fork, by dipping stuff in it, by tilting the bowl, ... Some would be considered gross, wasteful or painfully inefficient, but if it's just about what is possible, there's a lot more ways how to eat a soup.

So hence there are a lot of unstated premises and goals. It's assumed that it's not just about eating soup, but also about adhering to societal norms and so on or that you are interested in efficiency. Like it could be that using a machine to do chores is more efficient, but it could also be that you're not interested in efficiency but find some Zen in doing these things, so doing them faster is not even your goal.

So idk there are ideas like "if you buy a car you also need to buy fuel", which kinda make sense, assuming that you use it for the automotive purpose. So in that case it would not be a fallacy but rather playing captain obvious. While a collector might very well buy cars without even having a drivers license. So while not necessarily useful in the colloquial sense it's not impossible to do these things.

So whether the person has a point or not kinda depends on the concrete example.

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