Originating from the Italian word for "obligatory,” the musical term "obligato" traditionally refers to an instrumental or voice part essential to the integrity of a composition. In contrast, “ossia,” which comes from the Italian word for “alternatively,” refers to a musical passage that is an optional substitute for the main, notated part.

Obligatos are most associated with the Baroque music period, from about 1600 to 1750. However, music from later periods sometimes includes obligato parts, and they are still seen today.

Obligato parts often complement or contrast with the main melodic line. They are used to add depth and complexity to the music. Obligato parts also may highlight unique characteristics of specific instruments or voices and sometimes require significant virtuosity to perform.

Johann Sebastian Bach frequently used violin or oboe obligatos to enhance the vocal lines in his cantatas. His son Carl Phillip Emmanuel Bach used obligatos in his symphonies to designate woodwind parts being highlighted for the first time. Mozart used woodwind obligatos in his operas as counterpoint in his arias.

Ossias may either add or remove technical challenges for the musician. For example, Chopin included ossia parts to some of the more technical challenges in his Etudes. Berg's Violin Concerto has several ossia parts for the soloist, who, in effect, shares the solo violin part with the concertmaster.

However, in 20th-century music, the term “obligato” often is used for an option part that technically is an ossia. For instance, violinist Fritz Kreisler wrote optional violin parts, which he called obligatos, to accompany vocal music. Another 20th-century composer, Ernest Bloch, wrote a Serenade for String Orchestra, which includes an optional piano part he calls an “obligato.”

Contracts, real estate leases, and other legal documents also often include provisions that are mandatory (like obligatos) and/or are optional (like ossias). Terms such as "shall," "must," "will," "may," and "should” each convey different levels of obligation and discretion. Yet, legal documents or contracting parties often confuse or exchange these terms. This article discusses these terms and how to best use them in contracts and real estate leases.

Language that Creates a Contractual Obligation

Shall, must, and will are the most common contract terms used to convey that an action or obligation is mandatory. However, each has a subtle difference in meaning.

"Shall" denotes mandatory actions, requirements, or obligations a party must meet.

EXAMPLE: The tenant shall ensure that all real estate taxes and assessments are paid before the due date to prevent any penalty or lien from attaching to the Property,

Although “shall” is common in legal documents, outside of legal documents, “must” and “will” are more common. Given the trend to write legal documents in “plain language,” these alternatives to “shall” are becoming more common.

"Must" is used to denote a mandatory term. However, “must” indicates that a requirement is non-negotiable, unequivocal, and imperative. Although both “must” and “shall” describe required obligations. Most interpret “must” to convey more urgency and importance than "shall."

EXAMPLE: The tenant must pay all real estate taxes and assessments before the due date to prevent any penalty or lien from attaching to the Property.

Expressing Future Intention to Act in Contracts

Some people distinguish “shall” from “will,” claiming “will” indicates a party’s intention to perform a future act without imposing an obligation to do so. Under this analysis, “will” would be a weaker obligation than either “shall” or “must.”

However, it’s more accurate to interpret "will" as a command for a party to perform an act. When placed in a contract, that command becomes an obligation, making it a plain language alternative to “shall.”

EXAMPLE: “Tenant will install new carpet in the leased premises.”

If a party wants to express future intention to perform an act without explicitly imposing an obligation to do so, it’s best to say what the parties mean.

EXAMPLE 1: “Tenant intends to install new carpet in the leased premises.”

EXAMPLE 2: “Tenant expects to install new carpet in the leased premises.”

To make it clear the tenant isn’t required to install carpet, the lease could add “; provided, however, it will not be a breach of this lease if Tenant fails to do so.”

Using “Should” in Contracts

”Should” can be used more than one way in a contract. First, "should" can be used as a conditional verb. Therefore, some contracts use “should” as a substitute for “if.” That usage indicates a potential future circumstance that triggers a mandatory action.

EXAMPLE: “Should tenant receive notice of any health or safety violations at the premises, tenant will promptly notify landlord of those violations.”

In this instance, it’s better to use “if,” rather than “should.”

“Should” also can indicate an action is precatory, rather than mandatory.

EXAMPLE: “Tenant should promptly inform landlord of any maintenance issues.”

This example indicates no consequence if the tenant doesn’t make the notification. So, “should” expresses only a desired action rather than an obligation.

Had the above example included consequences for failing to inform the landlord of a maintenance issue, the provision would become mandatory. However, for a mandatory requirement, "must" or even "shall" are better choices.

Permissive Language in Contracts

Should is used in the lease example to describe an action the landlord requests but doesn't require. "May," on the other hand, would describe an action the landlord permits. Unlike “should,” “may” implies although the tenant has the option to act, landlord ambivalence as to performance.

EXAMPLE: “Tenant may, at its own expense, paint the walls in the Premises.”

Conclusion

Preparing and interpreting legal documents is more complicated than it looks. Seemingly insignificant language differences can significantly affect a contract's meaning.

In addition to subtle differences in English usage, statutes, and case law may affect how a contract must be written or interpreted. Sometimes, the law will even engraft meanings onto ordinary English terms that differ from their dictionary definitions or common usage.

Plus, contract provisions must be read in the context of the entire legal document and the parties' relationship using legal principles that may not be intuitive. So, even sophisticated parties who are even well-versed in the subtleties of the English language may find it challenging to prepare, review, and interpret legal documents.

Drafting errors can create ambiguity or unintended consequences, and errors in contract interpretation errors can result in unintended breaches. The result often is a legal dispute, which can lead to a breakdown in a business relationship and ultimately litigation.

Contracting drafting and interpretation aren’t just a science—they are an attorney’s art built upon years of study and experience. No matter how experienced or sophisticated an individual is, it’s best to consult with an experienced attorney before signing an agreement involving significant financial or personal commitment.

This series draws from Elizabeth Whitman’s background in and passion for classical music to illustrate creative solutions for legal challenges experienced by businesses and real estate investors.