Language components are the building blocks of ALGOL. They consist of basic symbols, such as digits and letters, and symbol constructs, which are those groups of basic symbols that are recognized by the ALGOL compiler.

<language component>

──┬─<basic symbol>─────┬───────────────────────────────────────────────┤
  └─<symbol construct>─┘

<symbol construct>

──┬─<define invocation>─┬──────────────────────────────────────────────┤
  ├─<identifier>────────┤
  ├─<number>────────────┤
  ├─<remark>────────────┤
  ├─<reserved word>─────┤
  └─<string literal>────┘

Basic symbols, identifiers, numbers, remarks, and string literals are described under separate headings in this section.

Because the define invocation is closely linked to the DEFINE declaration, the define invocation is explained in DEFINE Declaration.

Reserved words are described and listed in Reserved Words.