Before 1600, the OED gives citations where forty is spelled in various ways, but never with just an "o" vowel:
- feuortig, feortiȝ, fuwerti, uourty (the "u" is really a "v"), fourty, fourthi, fourtie
This might possibly mean that there was some actual diphthong leading to these spellings; since most of these spellings occurred before there was any standardization, it is hard to tell either way.
In 1600, there are three citations, and, interestingly, all of them have just "o":
- 1602 Contention Liberalitie & Prodigalitie i. iv. sig. B2, "Cham sure chaue come, vorty miles and twenty."
- a1642 J. Suckling Poems (1646) 37, "And there did I see comming down Such folks as are not in our Town Vorty at least, in Pairs."
- 1698 J. Fryer New Acct. E.-India & Persia 94, At the end of their Quarentine, which is Forty days.
(We can ignore the "v/f" alternation — something was apparently going with the voicing at the beginning of this word, but it probably has no bearing on the vowel following it.)
Aside from one citation in the 1700s that uses fourty, everything else from then on is written as forty.
One can only guess the reason for this change (at least with the information that I have) — whether it was pronunciation shifting or just orthographic simplification. But I might have an explanation for why this spelling took hold so swiftly in the 1600s: the Bible. The King James edition of the Bible was a major influence on the standards in English spelling. The KJV Bible was published in 1611 (begun in 1604), and (since I happen to have a KJV corpus handy) I see that there are 158 tokens with the spelling forty in KJV and 0 tokens for fourty.
So, even if the spelling of forty was following the whim of a handful of publishers, it got into the King James Bible, and that was that.
AmEng speakers do NOT use definite articles all the time; whether we do or not depends on what we want to say, and how we want to sound saying it. In particular, the use of the definite article with the present tense of the verb "to be" depends (in the words of a famous American) on what your definition of "is" is. Several of your example sentences sound distinctly unnatural to my USAite ear. Here are my suggestions based on my own usage:
School:
- He is in school. - He is a student; specific time does not matter. Perhaps it's Friday night and he's partying right now.
- He is in the school. - This does not sound natural at all to an American ear.
- He is enrolled in the school. - He is a student.
- He is at school. - He might be a student OR a teacher, but he is on the premises at this moment.
- He is at the school. - "The school" is a local landmark, and he's there right now.
Hospital:
He is in hospital. - He's an inpatient. This is valid, but not usual American usage. Anglophiles (Americans who like to drop Briticisms into their speech to appear more sophisticated) will sometimes use this.
He is in the hospital. - He's an inpatient.
He is at hospital. - We don't say this.
He is at the hospital. - He might be an outpatient, or he might work there; either way, he's there right now.
Church:
He is in church. - Services are in progress right now, and he's there.
He is at church. - Interchangeable with "in church".
He is in the church. - He's inside the building; no information is conveyed about what he's doing there (he might be polishing the floor, for example.)
He is at the church. - He's on the church grounds, not necessarily inside the sanctuary.
University/ College:
He is in university. - Americans don't usually say "in university"; "in college", however, means that he's a student.
He is enrolled in university. - He's a student.
He is at university. - He's a student. This is much more common than "in university", for some reason.
He is in the university. - Again, we don't say this.
He is at the university. - The university is a local landmark and he's there now. (Who is he - student, professor, tourist? Not enough information.)
Prison:
He is in prison. - He's a prisoner.
He is at prison. - We don't say this.
He is in the prison. - He's inside the building. He might be a prisoner, a warden, a visitor...
He is at the prison. - He's on the grounds, not necessarily inside the building - he might be waiting in the car while his wife visits her brother.
Best Answer
To use an s in specialised is usually the British English spelling. On the other hand, using a z is the American English spelling. You can choose which one to use depending on what your audience is. If you are in Europe, it may make more sense to use the British English spelling.
However, there is no such thing as one single, correct English. There are many, many dialects of English, and even what is known as Standard English varies between countries. If an American sees specialised, they will understand it, just as most British people would understand specialized. Both are versions of Standard English.