Mutably

Mutably is an adverb derived from the adjective mutable, meaning "subject to change" or "capable of being altered." The term describes an action performed in a manner that allows or permits modification of a subject’s state. In everyday usage it is often synonymous with "changeably" or "flexibly," though its application is especially common in technical fields such as computer science and legal drafting.

In programming, mutably refers to the ability to change data structures or variables at runtime. Languages that enforce strict mutability rules, such as Rust, provide explicit annotations for mutable and immutable references. Code that mutably borrows an object can alter its contents, whereas immutable borrowing guarantees no modification. For example, Rust’s &mut syntax denotes a mutable reference, allowing direct mutation of the underlying data. Many other languages use the simpler keyword "mutable" in variable declarations or function signatures to signal that a value may be modified.

In legal contexts, documents may use the term mutably to describe provisions that can be amended through later actions. Contracts may specify that certain clauses are mutably affected by regulatory changes, meaning the parties reserve the right to alter those clauses as laws evolve.

Historically, the concept traces back to Latin mutabilis, meaning "that may change," and found its way into English through Middle French and Latin-based legal and scientific vocabulary. The adverb mutably is relatively rare compared with the noun and adjective forms but remains useful when precision about the capacity for change is required.