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sequence

/ˈsiːkwəns//ˈsiːkwəns/·noun
a set of related things that follow one another in a particular order
Fig. 1 — Six steps stand in a rising staircase.
01Definition

A sequence is a set of things arranged one after another in a definite order, each following the last. From the Latin sequi, 'to follow,' it stresses succession: not just a group, but a group whose order is paramount. A sequence of events, a DNA sequence, a sequence of steps in a proof — change the order and the meaning can collapse. The word implies a thread running through time or space, where each element earns its place by what comes before it and what it makes possible next.

02In use
  • iThe detective reconstructed the exact sequence of events on the night of the crime.
  • iiIn a coherent argument, each claim follows the last in a logical sequence.
  • iiiMiss one step in the sequence and the whole experiment may yield an anomaly.
03Collocations
  • a sequence of events
  • in sequence
  • the correct sequence
  • a logical sequence
  • out of sequence

Family sequential (adjective) · sequentially (adverb) · sequencing (noun)

04Relations

=order, succession, series, progression, chain

≠randomness, disorder

06TOEFL & IELTS

Essential for narration and process description — TOEFL integrated tasks and IELTS Task 1 process diagrams both reward 'the sequence of steps'. Signposting words (first, next, subsequently, finally) build a sequence in Writing and Speaking. The adjective sequential ('sequential order') is common in academic English. Keep sequence (ordered succession) distinct from series (a set, order optional).

07Asked
What is the difference between a sequence and a series?
A sequence is an ordered list — things one after another, where order is the whole point. A series is what you get by adding a sequence's terms together, or, loosely, a set of related things where order may not matter (a TV series). In everyday use: a sequence of events is their chronological order; a series of events is just a run of them. The scene above is sequence exactly — six steps that light only in turn, no skipping.
What do 'in sequence' and 'out of sequence' mean?
In sequence means in the correct, intended order, each item following the last; out of sequence means jumbled, with something arriving before its turn. The phrases matter wherever order carries meaning — assembly steps, legal procedure, a story's timeline. Pages printed out of sequence are all present and useless, which is the point: a sequence is ruined not by loss but by disorder.
What does 'sequence of events' mean?
The order in which things happened, one leading to the next — the exact chain a detective, a report or an accident inquiry reconstructs. The phrase stresses causation carried by order: knowing what came before what is often the whole investigation. It is a staple of narrative writing, where laying out a clear sequence of events is the difference between a story and a heap of incidents.
What does 'sequential' mean?
Following in strict order, one after another — sequential steps, sequential page numbers, sequential access (reaching item five only by passing one to four). It is the adjective of sequence and the opposite of random or simultaneous. In academic writing 'in sequential order' underlines that the arrangement is deliberate, not accidental — each element earning its place from what came before.