Law relies heavily on documents, but is not a slave to them. In the early days of the American legal system, documents were in fact absolute. Even if they contained errors, the language of the document was considered binding. Over time, courts have taken a more relaxed view of documents, concentrating more on what the documents mean and how they reflect the real world when making their decisions on whether a document is legally binding.
One of the most important elements of a legal document considered when courts examine validity is the intent of the parties. Contract law specifically puts a strong emphasis on intent, saying that a contract must represent a "meeting of the minds." A contract can be invalidated or modified if it doesn't actually say what the parties agreed to and what they thought it said when it was executed. Intent is an essential element of all legal documents, from a will to a deed.
Another major feature of a document that influences whether it is legally binding is whether the parties had the authority or the standing to create the document. In contract law, a contract made by a minor or a mentally ill person, or even a normally competent person under the influence of drugs or alcohol, can be invalidated due to incapacity. In a will, for example, the testator must be "of sound mind and body." In other words, a person has to be capable of effectuating the terms of the document to make it legally binding. In a more extreme example, any person can draft a law, even a legislator, but it is not legally binding if it is not approved and passed by the legislative body, which collectively has exclusive capacity to make laws.
For a document to be legally binding it must be verifiably authentic. This is the reason documents are signed, witnessed and notarised. The process alone makes it difficult for the parties to later deny they signed a document. It also makes it less likely that anyone else could pass a false document as authentic. In probate, proving the authenticity of a will is one of the important tasks of the court. While some states allow spoken or handwritten wills, many require typed formal documents that can be properly witnessed to aid with verifying authenticity.
Another consideration is how well a document conforms with standard and generally accepted documents used to effectuate a particular intent. While it's not strictly necessary to use forms in all cases, using a form not only helps demonstrate intent, but also helps ensure that the document successfully encodes and reflects the intent. Contracts, for example, must be in plain and comprehensible language. A significant deviation from recognised document types can result in a document failing to be legally binding.
Another matter to consider is the time that has elapsed since a document was executed. In some instances, a document might specifically name a date or condition upon which it becomes invalid. This is not uncommon in contracts or leases. In other cases, the document might be superseded by a subsequent document or event, as frequently occurs with contracts and wills. Most states have laws that invalidate a will if the testator is divorced subsequent to its execution.