ISLOGICAL

What it does

ISLOGICAL(value)

ISLOGICAL(value) returns TRUE when the value it receives has kind Logical — that is, when it is the boolean TRUE or the boolean FALSE — and FALSE for every other kind.

Microsoft's condition: "Value refers to a logical value."

Logical is a distinct kind, not a number (the value universe). It converts to 1 or 0 on demand in arithmetic contexts, which is why TRUE+0 is 1 and SUM(TRUE) is 1, but the conversion is a coercion performed by the consuming function, not a property of the value. ISLOGICAL classifies before any of that happens, so:

• ISLOGICAL(TRUE) is TRUE
• ISLOGICAL(1) is FALSE
• ISLOGICAL("TRUE") is FALSE — the string, not the boolean
• ISLOGICAL(1=1) is TRUE — comparison operators produce Logical values

The last line is the useful one: ISLOGICAL is the way to confirm that a comparison, a NOT/AND/OR result, or an ISxxx result really is a boolean and not a number that happens to be 1 or 0.

Arguments

value — required, exactly one.

Not converted. Microsoft's remark: "The value arguments of the IS functions are not converted." The to-logical primitive described in coercion and lifting — under which zero becomes FALSE, nonzero becomes TRUE, and in some contexts the strings "TRUE"/"FALSE" are accepted — is exactly what ISLOGICAL does not do. Whether text that names a logical is accepted at all is per-family policy elsewhere in Excel; here it is settled, because no conversion is attempted.

Try it

Quirks

Result and edge cases

Returns a Logical, or an array of Logical when the argument is an array.

• FALSE is a logical. ISLOGICAL(FALSE) is TRUE. The predicate is about the kind, not the truth value, and an implementation that special-cases falsiness will get this wrong.
• 0 and 1 are FALSE. Numbers, whatever their value.
• The strings "TRUE" and "FALSE" are FALSE. They are Text.
• Empty is FALSE. A blank cell is not a logical, even though most boolean contexts treat it as FALSE.
• Error is FALSE and does not propagate; ISLOGICAL is one of the declared per-family exceptions to the propagation discipline in coercion and lifting.
• Logicals in scanned ranges are ignored by some aggregates even though they are present as values. That is a scan-policy fact about SUM and friends, not about ISLOGICAL, but it is the same underlying kind distinction seen from the other side, and it is why a column of TRUE/FALSE can be simultaneously "logical" to ISLOGICAL and invisible to SUM.
• Arrays are classified elementwise into a same-shaped mask.

Errors

Microsoft's IS-functions page documents no error return for ISLOGICAL.

How to implement

Notes for implementers

1. Model Logical as its own kind. An engine that represents booleans as numbers 1 and 0 cannot implement ISLOGICAL at all, and cannot implement TYPE either. This is the single design decision the function polices.
2. Do not accept "TRUE"/"FALSE" text. The to-logical primitive's text acceptance is per-family policy elsewhere; it must not leak into a kind test.
3. ISLOGICAL(FALSE) must be TRUE. Worth an explicit test, because a naive "is it truthy?" shortcut passes every other case.
4. The kind must survive comparison operators. 1=1 has to produce a Logical, not a number, or ISLOGICAL will report FALSE on the most natural way of producing a boolean.

Rust code

unary(ISLOGICAL, "ISLOGICAL", VALUE, islogical)

/// ISLOGICAL: TRUE for TRUE and FALSE; their text is text.
fn islogical(
    arguments: &[CalcValue],
    services: &mut EvalServices<'_>,
) -> Result<CalcValue, FunctionFault> {
    predicate(ISLOGICAL, arguments, services, scalar, |core| {
        matches!(core, CoreRef::Logical(_))
    })
}

No implementation has been published with a Handbook test suite for this function.

Version differences

The recorded environments below distinguish a reading from a same-input comparison. Counts describe captured inputs in each environment; overlapping captures and comparisons are not totals of unique worksheet calls.

The record contains no same-input comparison between these environments. Reading different inputs on different builds does not establish either a version change or cross-build agreement.

Recorded environments and comparison details.

Alternatives

Relationships

• TYPE returns 4 for exactly the values ISLOGICAL calls TRUE. 4 is the odd number out in the TYPE code table — 1, 2, 4, 16, 64 — and the gap at 8 is a reminder that these are bit flags by origin.
• ISNUMBER is the predicate people reach for when they want "is it 1 or 0 or TRUE or FALSE?" and it will not give them that; ISNUMBER(TRUE) is FALSE and ISLOGICAL(1) is FALSE, so neither predicate alone covers the union. OR(ISNUMBER(x), ISLOGICAL(x)) does.
• N converts a logical to 1 or 0 — the conversion ISLOGICAL declines to perform. N is the standard way to turn a Logical mask into a summable numeric mask, as is the double unary --.
• TRUE() and FALSE() manufacture the values this predicate tests for.
• ISNONTEXT is TRUE for logicals too, but for six other kinds as well; ISLOGICAL is the precise test.

Named variants

No named variants are recorded yet.