According to Merriam-Webster, “income tax” is a synonym of “value-added tax” and “property tax”. And it can be, depending on context, but few people would argue that they are always synonymous. It’s the same with “tariff” and “tax”. Whether or not they are synonymous depends on context.
My point exactly. The bet was about whether “tariff” and “tax” are synonymous. They aren’t synonymous if they describe different things, even if one of those things is a subset of the other. (This is complicated a bit by the fact that synonymity is context-dependent so in some contexts they can be synonymous. I’m assuming a general context.)
To give a different example, every iPhone is a smartphone but not every smartphone is an iPhone. The two terms aren’t synonymous except in specific contexts like when discussing the inventory of an Apple store.
In a general context, I would argue that the bet is lost – tariffs are taxes but taxes encompass more than just tariffs. The definition of synonymity is not fulfilled.
The actual point of the bet, namely to illustrate that tariffs are paid by people in the country that raised them (because they are taxes on imported goods and services), remains valid.
I would’ve made you pay him. Every tariff is a tax but not every tax is a tariff. Of course your actual point still stands.
There are various definitions of synonymity with varying degrees of strictness. Whether something is considered synonymous depends both on how strictly one defines synonymity and on which context one operates in.
I assumed a relatively strict definition: Two terms are synonymous if and only if they can be used interchangeably in most contexts, e.g. “bigger” and “larger”. Under that definition, “tax” and “tariff” are not synonymous; “tariff” usually implies something crossing a border while “tax” doesn’t.
However, an equally correct definition is that two terms are synonymous if they have similar or related meanings within a context. Under this definition, “tax” and “tariff” are synonymous since they describe similar things – even if they aren’t interchangeable. This definition is usually used by synonym lists because it makes it a lot easier to write those lists. Annoyingly, this means that two words that are listed as synonymous in such a list aren’t necessarily synonymous in the context you’re using them in.
For example, Collins lists “tariff” and “tithe” as synonymous. Do you know anyone who pays a tariff to a church? The synonym list for “tithe” doesn’t even mention a church-specific reading; it just assumes that a tithe is some kind of tax and that’s close enough. You can write like that but your style would be seen as very flowery and wouldn’t be suitable e.g. in a scientific context.
Another correct definition, by the way, is that the two words must have exactly the same meaning in all possible readings. That one is so strict it’s practically useless for natural languages but can be use in different contexts.
Let’s look at how Merriam-Webster describes synonyms:
All three definitions I gave above match Merriam-Webster’s first definition, depending on whether one chooses “the same” vs. “nearly the same” and “some” vs. “all”.
Interestingly, Collins’s definition of “synonym” is very strict due to excessive brevity:
This doesn’t allow for similar meanings (which their own synonym lists heavily rely upon as illustrated above), which is probably not intended.
I didn’t check Thesauris since you messed up that link but so far one dictionary says “it depends” and the other one says “the meaning must be the same” (and then completely ignores its own definition). “It depends” is the best we can do.