"Polarizes" is not the right word for this. If you can imagine a group of people being strictly divided in opinion, the ideological line which divided them would be the thing I am trying to generically name. I'm looking for a specific word that I know I've seen before but can't remember. I've googled this but have not been able to find the right word. This is the best definition I can provide.
An (poor) example is how a stance on taxes divides people into Democrats and Republicans
Perhaps the word you are looking for is shibboleth:
a custom, principle, or belief distinguishing a particular class or group of people, especially a long-standing one regarded as outmoded or no longer important.
(from the Oxford Dictionaries web site). The word means "ear of corn" in Hebrew; it was considered difficult for foreigners to pronounce properly, so the Gileadites used it to detect Ephraimite refugees and slay them. See Judges Chapter 12 for the full story.
If you are looking for an adjective I think you may use divisive:
- causing a lot of disagreement between people and causing them to separate into different groups.
(M-W)
A wedge issue is one which actively (as opposed to passively) divides people into polarized groups. A typical one in American politics is abortion, another is gun control.
A wedge issue is a political or social issue, often of a controversial or divisive nature, which splits apart a demographic or population group.
https://en.wikipedia.org/wiki/Wedge_issue
If you are looking for a noun for the division (besides division), perhaps you are thinking of schism? Google defines it as
a split or division between strongly opposed sections or parties, caused by differences in opinion or belief.
At one time it applied more specifically to divisions within a church, and that's still sometimes the first definition in dictionaries1, but I think Google's definition captures a fairly common popular usage. The implication of a very deep division based on an ideological difference of opinion would seem to suit your question.
Usefully, according to the OED this noun has already been verbed:
Obs. rare. intr. To separate schismatically.
1604 H. Jacob Reasons 77 He that differeth from the Gospell ioyneth not to the Church, but schismeth from it.
And there is also the much more common adjective, schismatic.
Thus you could say something like
The schism between Republicans and Democrats over taxation seems unlikely to resolve anytime soon.
Or
Congress has schismed over the issue of taxation.
Or
The schismatic issue of taxation is polarizing voters.
I'm not 100% sure of what you want but if none of the above answers fit, what you might want is "litmus test" in the following senses:
From Merriam-Webster: a test in which a single factor (as an attitude, event, or fact) is decisive
Or: From Wikipedia: a question asked of a potential candidate for high office, the answer to which would determine whether the nominating official would proceed with the appointment or nomination.
It is, of course, used as an analogy to the litmus test in chemistry to describe a question or issue that divides people into two camps.
Common words to describe a "an opinion on a subject which, by definition, divides a group of people", would simply be controversial or confrontational.
If not, I take the description to mean they are entrenched in their positions, so that 'idealogical' line might reference their impasse. There's a 'line in the sand' so to speak.
You said you couldn't use it in a sentence, so I'm trying to think of different ways to describe these groups, their 'demarcation' (as above), or a description of their incongruent positions.
His opinion on the matter was controversial.
These two groups of people would be at an impasse.
Their idealogies are incongruent.
They might be two disparate groups.
An ideological fault line is often used to describe a gap in politics between two groups. For instance:
The ideological fault line between Republicans and Democrats often comes down to whether they feel income redistribution by tax is just.
The word bellwether is often used to describe an issue that is useful for disambiguation of whether an individual or group is on one side a fault line or another, and need not be directly related.
"Love of travel is a bellwether of whether someone will vote Republican or Democratic." Abe asserted, perhaps jokingly. "But then again, existence of toenail fungus is also a political bellwether."
Used in aggregate, to map one trait of a group to another:
High unemployment is a bellwether that a group will vote a Libertarian into office.
Demarcation as a noun, and demarcate or demark as a transitive verb come to mind.
demarcate: to delimit or set apart (Merriam Webster), or ~1.1 to separate or distinguish from (OED)
demark: another term for demarcation.(OED)
demarcation, ~1.1 a dividing line (OED)
So, for example, you could say something like "Republicans and Democrats are strongly demarked by their attitudes towards taxation" or perhaps "Attitudes towards gun control form a strong demarcation between different segments of society".
demarcated is less awkward and used more often than demarked. "The wall demarcated the border with Canada."
Commented
Jul 12, 2016 at 20:32
Many of the other answers would fit the question -- but if you're looking to describe an issue so polarizing & divisive that it would cause an argument or fight, I'd go with contentious.
A cleavage or a cleaving issue: New Yorker cover shows Donald Trump cleaving the GOP elephant. Cleavage (MW):
a division between two things or groups
cleavage is the division of voters into voting blocs
In cross-cutting cleavage one finds:
"Cleavages" include such things as racial, political, religious divisions in society
Here are some uses in context:
Using your example “A stance on taxes divides people into Democrats and Republicans”, of the few verbs that come to mind (partition, segment, and segregate), segregate seems best:
A [particular] stance on taxes segregates people into Democrats and Republicans.
Based on the question, it seems likely that you are looking for a nounal (or potentially adjectival) form to describe the kind of thought, idea, or view that would divide or distinguish people. For that, the word distinctive seems appropriate: e.g. …
Among historic Calvinists and Puritans, the doctrine of the exclusive baptism of believers (and that by immersion) is a Baptist distinctive.
See also examples of pages that outline doctrinal differences calling them “distinctives”: Presbyterian Distinctives, Historic Baptist Distinctives.
You're asking for a verb that would mean "to divide based on opinion," but what you should be looking at is adjectives to describe a verb, since we don't really have a word for that.
An opinion(noun) can be polarising. ("can be polarising" is the verb phrase here.) Maybe the opinion that was expressed in Carl's speach divided the people. ("divided" is the verb which the subject "opinion" does to the object "people")
"He gave a polarising speach." speach is a noun in this past-tense descriptor.
It sounds like you are looking for the word issue: whether taxes should be equally applied to rich and poor, or scaled, is the issue that divides Democrats and Republicans.
