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Specifications Language: The Meaning of “Shall,” “Will,” and “Must”


Editor's Note: CSI is pleased to publish this blog from Kevin O’Beirne, PE, FCSI, CCS, CCCA, CDT. If you have an idea or opinion you would like to share with your colleagues in the construction industry, please contact CSI Content Strategist Peter Kray at He would love to help publish your thoughts.


Attorneys and drafters of contracts, including construction specifications, periodically debate whether the words, “shall,” “will,” and “must” are appropriate in contracts. The arguments never end. This writer has read various articles by attorneys presenting opinions on the subject, but most omit a detailed discussion of the words’ actual meaning.  Because “shall,” “will,” and “must” are used in articulating key contractual obligations, it is important to use them properly.


The brief essay, “Shall and Must”, on and circulated by AXA XL Insurance to its professional liability insurance customers in 2019, includes:


“Use ‘must’ not ‘shall’ to impose requirements. ‘Shall’ is ambiguous, and rarely occurs in everyday conversation. The legal community is moving to a strong preference for ‘must’ as the clearest way to express a requirement or obligation… For a good discussion of ‘shall’ and ‘must’, see Bryan Garner, A Dictionary of Modern Legal Usage (2d ed. 1995), pages 939-942.”


Unfortunately, aside from citing attorney Garner’s work, the essay provides little more than unsupported assertions and broad opinion. As presented below, this writer does not see how “shall” is unclear; rather, “shall” is a clear command and clearly communicates an obligation, and “will” should also not be tossed on the scrap pile of contract language.


The Construction Specifications Institute’s (CSI) recommendations on specifications language are set forth in CSI’s Construction Specifications Practice Guide, First Edition (“CSPG1”, 2011) and the Project Delivery Practice Guide, Second Edition (“PDPG2”, 2018).


CSI recommends using, “the imperative mood,” in construction contract language. CSI encourages specifiers to write requirements as, “Provide bricks…” rather than often repeating, “Contractor shall,” i.e., “Contractor shall provide bricks…”


Specifiers cannot always avoid using “Contractor shall” or its derivatives such as “Owner will,” especially when specifications address requirements of both parties, and perhaps of others. For example: “Owner will remove the debris pile after which Contractor shall provide the foundation.” Recommended language style and use of “the imperative mood” is addressed in CSPG1 Sections 1.5 and 2.3, and PDPG2 Sections and through


CSPG1 Section 2.3 states in part:

 “Shall and Will are used as imperatives in reference to the work required to be done by a contractor. Will is optional and is used in connection with acts and actions required of the owner or the architect/engineer (A/E).

Must and ‘is to’ are not recommended.”


While the CSPG1 appears definitive, it presents no rationale or citation to support its assertions on this matter. Furthermore, there is copious evidence that “must” is widely used in contracts and specifications.


Obviously, “will” is not the only expression relavant to the owner or its design professional.  In many instances, “shall” is entirely appropriate in connection with the owner, such as: “Owner shall pay the Contractor the amount recommended by Engineer, prior to the date such payment becomes due.”  There should not be much discretion regarding the owner’s obligation to pay its contractors amounts not subject to disagreement. In other cases, “will” may be entirely appropriate to use in relation to the contractor.


CSI’s PDPG2 (2018) includes multiple examples of appropriate phrasing for construction documents in its Sections through but, interestingly, does not directly address uses of “shall,” “will,” “must,” and “is to”.


When in doubt, check a widely-used dictionary. Black’s Law Dictionary, Tenth Edition (2014), does not address “must” but includes:

  • “Shall: Has a duty to; more broadly, is required to… This is the mandatory sense that drafters typically intend and that courts typically uphold…”
  • “Will: Wish; desire; choice..” [e.g., a last will and testament].


The American Heritage Dictionary, Second College Edition (1985) is the ordinary dictionary on this writer’s office shelf. It includes:

  • “Must: 1. To be obliged or required by morality, law, or custom.  2. To be compelled as by a physical necessity or requirement… 3. Used to express a command or admonition…”
  • “Shall: 1. Used to indicate simple futurity: ‘I shall be 28 tomorrow.’  2. Used to express: a. determination or promise: ‘He shall answer for his misdeeds.’ b. Inevitability: ‘That day shall come.’ c. Command, ‘Students shall report weekly to their tutors.’ A directive or requirement. ‘The penalty shall not exceed two years in prison.’…”
  • “Will: …2. An instance of exercising will or choice.  3. Something desired or decided upon by a person of authority or supremacy.  4. Deliberate intention or wish. 5. Discretion; inclination… 6. Bearing or attitude toward others; disposition.  7. The power to arrive at one’s own decision to act upon it independently, despite opposition.”


Based on Black’s Law Dictionary and American Heritage Dictionary, we may conclude: 

  1. “Must” appears appropriate to use in contracts and specifications as a command or to communicate a requirement.
  2. “Shall” appears appropriate to use in contracts and specifications as a command or to communicate a requirement. It may be at least as clear for this as “must”.
  3. “Will” is perhaps less clear and appears to imply some level of discretion by the entity to which it applies. However, when properly used, “will” can be clear and used to create binding obligations, as discussed in attorney Bryan Garner’s book cited above. Despite this, this writer believes “shall” creates a level of gravity and formality that is entirely appropriate for the duties of the parties to a construction contract or design professional services agreement.
  4. “Is to” may be grammatically correct but, in a contractual sense, appears to lack the gravity and command communicated by “shall” and “must”.


Admittedly, the above does not consider case precedents or sources other than those expressly cited, and one of the dictionaries referenced is quite old. It may be unwise to stress your brain on this, because EJCDC C-700—2018, Standard General Conditions of the Construction Contract, Paragraph 1.02.G, says:

“Unless stated otherwise in the Contract Documents, words or phrases that have a well-known technical or construction industry or trade meaning are used in the Contract Documents in accordance with such recognized meaning.”

Virtually identical wording is in Section 1.2.3 of AIA A201—2017, Standard General Conditions of the Contract for Construction.  Thus, the meaning of “shall”, “will”, and “must” can be revealed by consulting a dictionary. 


In drafting contracts and specifications, remember that words have specific meaning and should be employed properly. So much for my opinions on “shall”, “will”, “must”, and “is to”.  Let the debate continue!


Kevin O’Beirne, PE, FCSI, CCS, CCCA is a professional engineer licensed in NY and PA with over 30 years of experience designing and constructing water and wastewater infrastructure for public and private clients.  He is the engineering specifications manager for a global engineering and architecture design firm.  He is a member of various CSI national committees and is the certification chair of CSI’s Buffalo-Western New York Chapter.  He is an ACEC voting delegate in the Engineers Joint Contract Documents Committee (EJCDC) and lives and works in the Buffalo NY rea.  Kevin O’Beirne’s LinkedIn page