Overview

In every society, agreements must be made, and some must be enforceable. Enforcement varies by society - in Astrum, the fallout from violating one's word may be dishonor, social or actual exile, etc. In Gaean, it may be fines, imprisonment and the like. Incaendium is no different - a legally binding contract signed on paper can be legally enforced, yes... but for those who do not want to risk the trouble of betrayal and enforcement, there is also the Binding Contract.

Rules and Requirements

Necessities in forming the Contract

The contract must be formed between at least two people, with no upper limit.
In theory it would be possible to use a binding contract to ensure permanent loyalty to a specific leader, for example, though in practice this is practically impossible because of the requirement of true agreement.

Willingness & Regret

A Binding Contract is a magically enforced agreement between willing parties.

That it is voluntary is the only true rule of a Binding Contract: any substantial resentment or reluctance (as would occur as a result of, for example, coercion, threats or force of any kind) will prevent the magic from taking root and building the bind between the parties.

Note that this only has to be true at the time of forming the contract. That being the case, it isn't uncommon for people to regret choices made in ignorance, thoughtlessness or as a result of lies or manipulation, only to find themselves trapped inside that agreement nonethless.

At least one of the people must have the ability to Void-Dance and the knowledge of how to weave this specific magic.
It does, of course, require stronger magic in accordance with the size of the agreeing party, but the spell itself is not especially taxing, so it would take a great many people to become problematic.

All persons involved must understand the terms of the contract.
This includes everything they are expected to do and what they are expected to receive in return (assuming it is a transactional contract) or any other relevant requirements or guarantees baked into the contract. This also includes the terms for dissolution of the contract. More on this later.

Examples of Contract Use

Some common varieties of Binding Contract are listed below. Bear in mind that these are just examples, and the contents of the agreement are entirely up to the parties involved.

Employer/Employee Contracts
Used to stipulate things like duties, compensation, length of guaranteed employment.

Professional Partnership Agreements
Stipulating things like who is responsible for what part of the project/business and profit splitting. This is also used by adventurers sometimes before they go into a dangerous mission.

Hari Suum Contracts
In fact, binding contracts are necessary in order to be considered a Hari Suum - though the specifics of the contract can vary by person.

Secrets Keeping
An excellent way to keep a terrible secret from being spread around!

Shaping the Nature of the Binding Contract

The magic that forms the Binding Contract does have some default characteristics. However, these characteristics are mutable with specified clauses inside the casting of the contract spell.

Example of a Binding Contract

Parties involved
An employer and a craftsman.
Requirements
The craftsman must design and fashion new bedroom furniture. The employer must pay the agreed upon sum of 5,000 Aline.
Consequences of Non-Compliance
The non-compliant party will have a constant unbearable itch in the one place on their body they would find most embarrassing to scratch (wherever that is!) until the task is done.
Dissolution
Fulfillment of the contract terms.
Consequences for Non-compliance

If not specified, the contract enforces through compulsion. A person will feel an overwhelming need to do what they have sworn to do - a drive that deepens as the action goes unfulfilled until it essentially morphs into a geas. By contrast, when one has agreed not to do something, the agreeing person will simply be unable to do that thing - as though there is a complete collapse of executive functioning on that topic alone.

That said, it is common to override these defaults with other consequences that are more appropriate to the specific contract.

  Ending the Contract By default, a binding contract is permanent. However, this is rarely left intact during the formation of the agreement, for obvious reasons. This does require that the means and conditions of termination must be directly specified. Typically this will be something like "completion of the task," a certain period of time or "the agreement of (one or both) parties."

A Realistic Assessment

Well, the option for binding contracts exist. So, how common are they, really, among demonkind?

...not very.

Demons dislike making promises as they prefer to follow wherever their passions lead them even if it means breaking a promise and getting into a physical fight over it. Generally, these contracts will be made with non-demons, when the demon wants something from said non-demon.

The primary exception to this is the contract that exists between a Dominus and a Suum (a servant unable to leave service by their own will alone.). Typically a Suum contact will have a time period or specific requirements to fulfill, as well as a caveat that the Dominus can dissolve the contract at will.