A little lesson in linguistics, or the people first shibboleth.

Chomsky notwithstanding (who talks of a technical reconstruction of syntax rather than a pedaogogical grammar ) The reality of  grammar in terms of "people first" language means less than the actual usage and it's connotations. That is to say the communicative intent and how it is understood in any particular community always takes precedence over any strict 'by the book' rule

I do not have sufficient knowledge of comparative linguistics to really analyse the way things can be said in languages that don't permit the same grammatical forms and alternatives as English. The very flexibility of English as a polyglot language encompassing more one grammar and vocabulary is partially what allows these distinctions, though the distinctions would still exist independently of language, only un-named and categorised, the fact that something is either named (or described) or not being in itself indicative of the social status of such a difference being expressed in the alternative forms

Anyway consider this description

"I am a convict."

That sounds pejorative -  I am someone who has been caught committing a crime and have been sentenced.

However, as any thesaurus will tell you, conviction bears alternative meanings. Consider further for example

"I am a person with conviction"  or "I am a person with convictions"

Very similar phrases we the second being merely a plural of the first. However but the context and conventional usage makes other distinctions. For instance the connotations of the first are fairly unambiguous that I am a person who 'is convicted, or convinced, a person who holds deeply entrenched beliefs  the most common instance being religious convictions. On the other hand the second phrase does not so readily (although it can) add a plural to, introduces an ambiguity that implies I am more likely to be a person who has been through the courts than a person who has more than one set of strongly held beliefs.

I can use a similar phrase using a similar word.

"I am a conscript" Which would be clear enough to understand that I am a person who has been conscripted into the armed forces, but to say I were 'a person with conscription ',  'a person with a presecription' or even 'a person who has a conscription'  that would appear to be rather nonsensical since the English language does not use a noun conventionally to describe the state of being conscripted,  conscription referring to the process rather than any single artefact one can posses like a 'prescription'

Turning it around then I could say though that I were a person with a prescription, but not a person with prescription. I can be a prescribed person though, which is entirely different to being a proscribed one, it's close homophone.

Well getting round to the argument by a difficult route.

I can be a described person and equally a person with a description. Disability or Autism being in this instance of the category 'description' not 'entity'

What all the foregoing really demonstrates is that there are no hard and fast pedagogical rules, only conventional usages and understandings one learns and uses in context. It's more idiom than strict grammar.

In the wider scheme of things it has nothing to do with any grammatical difference in the meaning if the adjective comes before the person, or after, because formal rules allow either. However the social use of language has determined something beyond grammar in determining whether a person is a disabled person, or a person with a disability because those two differences are in a sense shibboleths which determine or betray a lot more than the meaning of the phrase itself.

I have searched hard for a succinct summary of the difference and the best I can find comes ironically from the last place one would expect a style guide for 'political correctness' the Rugby Football league's style manual.

"Disabled people / person /spectator is the preferred term and the term used by the RFL as this reflects the social model of disability which emphasises that people with impairments are disabled by society not by their impairment. For example “Wheelchair users can’t use the facilities because the venue is inaccessible; therefore, we need to modify the building and the services we provide.”

The social model was not developed as some form of “denial” of impairment, it was developed in order to inform society, which includes disabled people, of the real reason that individuals are not able or allowed to take a full and active role in society. It follows then, if society in general, organisations and those individuals working within them acknowledge, understand and implement the ‘social model’, there would be far less discrimination against disabled people and greater access to services and the society as a whole.

Person with a disability is a medical model perspective which implies a person’s impairment or medical condition causes the disability. You firmly attach the disability to the person with this phrase when it’s not it’s with society. For example “Wheelchair users can’t use the facilities because of their impairment, as it prevents them from getting up the steps at the entrance of the venue”.You will come across many people, disabled and non-disabled, who use language we advocate avoiding i.e. people with disabilities. Firstly they may not know about the social model but also may choose to be referred to in a particular way. Where it is not appropriate to challenge (sometimes it will be) promote the use of preferred terminology through your own use and certainly in any marketing material that is produced."

Further musings on why 'people first' language is merely a pretence that enshrines discrimination rather than confronts it can be found in Jim Sinclairs classic piece which bears repeating in full:

"I am not a "person with autism."   I am an autistic person.  Why does this distinction matter to me? 

1) Saying "person with autism" suggests that the autism can be separated from the person.  But this is not the case.  I can be separated from things that are not part of me, and I am still be the same person.  I am usually a "person with a purple shirt," but I could also be a "person with a blue shirt" one day, and a "person with a yellow shirt" the next day, and I would still be the same person, because my clothing is not part of me.  But autism is part of me.  Autism is hard-wired into the ways my brain works.  I am autistic because I cannot be separated from how my brain works.

2) Saying "person with autism" suggests that even if autism is part of the person, it isn't a very important part.  Characteristics that are recognized as central to a person's identity are appropriately stated as adjectives, and may even be used as nouns to describe people: We talk about "male" and "female" people, and even about "men" and "women" and "boys" and "girls," not about "people with maleness" and "people with femaleness."  We describe people's cultural and religious identifications in terms such as "Russian" or "Catholic," not as "person with Russianity" or "person with Catholicism."  We describe important aspects of people's social roles in terms such as "parent" or "worker," not as "person with offspring" or "person who has a job."  We describe important aspects of people's personalities in terms such as "generous" or "outgoing," not as "person with generosity" or "person with extroversion."  Yet autism goes deeper than culture and learned belief systems.  It affects how we relate to others and how we find places in society.  It even affects how we relate to our own bodies.  If I did not have an autistic brain, the person that I am would not exist.  I am autistic because autism is an essential feature of me as a person.

3) Saying "person with autism" suggests that autism is something bad--so bad that is isn't even consistent with being a person.  Nobody objects to using adjectives to refer to characteristics of a person that are considered positive or neutral.  We talk about left-handed people, not "people with left-handedness," and about athletic or musical people, not about "people with athleticism" or "people with musicality."  We might call someone a "blue-eyed person" or a "person with blue eyes," and nobody objects to either descriptor.  It is only when someone has decided that the characteristic being referred to is negative that suddenly people want to separate it from the person.  I know that autism is not a terrible thing, and that it does not make me any less a person.  If other people have trouble remembering that autism doesn't make me any less a person, then that's their problem, not mine.  Let them find a way to remind themselves that I'm a person, without trying to define an essential feature of my personhood as something bad.  I am autistic because I accept and value myself the way I am." copyright Jim Sinclair 1999