The language of magic is common enough that the upper middle class and idle rich like to impress each other at parties with their so-called knowledge of the secret tongue.
This cause mages to seek out areas of refuge away from anyone speaking magic. Otherwise, they could inadvertently begin casting spells and nobody wants to do that by accident!
In cities, mages organize network of so-called Quiet Areas. These quiet areas are areas safeguarded against anyone that would speak magic, even other mages. If a Quiet Area cannot be found, a good mage always has the ability to use two helpful and relatively inexpensive magic items. The first silences the area around where he is sleeping. The second locks the door. Wholesale manufacture of magical items is rare. These two items are a noted exception - they are created by mages for mages. They are not made available to anyone that does not practice magic.
As a mage increases in power, these magic trinkets and even the Queit Ares tend to become less effective. The growing need to avoid accidental spell casting drives a mage to build a stronghold away from other people.
This is the primary reason why mages, as they get more powerful, have less to do with people and the real world and seek refuge their stronghold. Many even escapes to the various planes that float along the Astral Sea.
Another effect of the common knowledge of the language of magic is that all magic items have a code word to activate. Weaker items usually have easy-to-guess code phrases. Any fighter with experience can usually guess the code phrase for weaker magic items.
In a d20 based system, determine the DC for a mage to get the code word, divide the cost of the item by 100. That provided the DC to beat on a d20. For those using ACKS, a limited ability to guess activation words is included in the Adventuring proficiency.
Since the knowledge of the language of magic does not grant the ability to use magic, a would-be magic user has two options. The most popular option is to join a temple and offer your services as an emissary. Emissaries, often called clerics, are given a measure of power by a deity in exchange for service. This arrangement usually works out well for both deity and cleric. However, due to a large number of potential applicants, clerics do not gain the ability to use divine power right away. A cleric must go through a time of testing to prove their devotion.
There are a number swordsmen and military men in urban areas that left the temple before gaining the ability to use divine power. Their lack of faith makes them a bit resistant to divine magic, including any healing magic.
For those using ACKS, this is a new proficiency called Lack of Faith. It provides a small bonus (+1 or +2) for saving throws against all divine magic. It also forces a character to make a saving throw against healing spells to be healed.
For those that want the ability to wield magic, but do not have the desire (or faith) to join a temple, there is only one option: psionics. The Science of the Mind holds the promise of allowing anyone to harness the power of magic that exists within themselves. In that sense, psionics are nondiscriminatory. The difficulty for the would-be psion is that not all teachers that claim to know the science actually do.
Finding a teacher that can actually imbue psionic power is difficult in urban areas. It is almost impossible in more remote areas. It takes a powerful psion to provide the training and the ability.
For those using ACKS, only a 9th level or greater psion can imbue power. Imbuing the ability is a power a high level psionicist must learn to use. The cost is great and can be done a limited number of times in a psionicist's life.
The drawback to being a psionicists is that it is a one way trip. Once a person becomes a psionicist, he or she can never become something else. No temple, even the most inclusive ones, will ever admit a psionicist as a cleric. Without the ability to use magic, there is no option to become a mage. Psionicists are not trusted by fighting men and will not be trained.
The other cost for learning psionics is tremendous difficulty with the language of magic. Whereas anyone else can learn and speak the language of magic with realtive ease, the act of gaining their power removes this ability. This also prevents them from using their Suggestion power and "placing" magic phrases into a mage's mind while he/she is asleep in order to trigger a spell.
Psionicists are not driven to seclusion by their power. Unlike mages that are born to their power, a psionicist chooses theirs. Their power is not bound to
a certain language or phrase. In fact, many psionicists tend to enjoy people and crowds as they gain power. Instead of building strongholds and castles, they build schools and train others.
The schools are not publicly advertised. Many temples actively seek to destroy such schools. These schools are seen as destroying the faith of the weak-minded. To a cleric, true power comes from a deity, not from within.
Mages tend to see psionicists as second-class spell casters. A common expression is "those that can't do, teach" often used as a pejorative. To a mage, the powers of a psionicist can be either duplicated by magic (ESP, Clairvoyance, Telekinesis) or are not very useful (Postcognition). There are limited battle powers available to a psionic. A mage can easily prevent their thoughts from being read by a psionicist without resorting to magic. (This last statement is often repeated, but not entirely true. The mage chooses to think in the language of magic thereby preventing a psionicist from understanding a mage's thoughts. However, thinking in the language of magic requires a lot of concentration to prevent a spell from being cast by accident.)
The rest of society does not see any difference between the three methods of using magic. To them, having the power is a price too high, even in a world with supernatural creatures.
Clerics always build strongholds near populated areas. More followers = more power.