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In PHP, true is a reserved keyword and a boolean literal representing the affirmative truth state in boolean logic. It is one of the two possible states of the scalar bool data type, the other being false.

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Syntax and Case Sensitivity

The true literal is case-insensitive. However, the PHP-FIG PSR-12 coding standard mandates the use of strictly lowercase letters for all reserved keywords, including boolean literals. 
$a = true;  // Standard (PSR-12 compliant)
$b = TRUE;  // Valid, but non-standard
$c = True;  // Valid, but non-standard

var_dump($a === $b); // bool(true)

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Type Coercion and Casting

When PHP’s Zend Engine coerces or explicitly casts the true literal into other scalar or compound types, it follows strict internal conversion rules:
  • Integer: Casts to 1.
  • Float: Casts to a floating-point 1.0 (Note: var_dump outputs whole-number floats without the .0 decimal).
  • String: Casts to "1" (Note: false casts to an empty string "").
  • Array: Casts to an indexed array containing the boolean as its single element at index 0.
var_dump((int) true);    // int(1)
var_dump((float) true);  // float(1)
var_dump((string) true); // string(1) "1"
var_dump((array) true);  // array(1) { [0]=> bool(true) }

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Comparison Mechanics

Because PHP is a dynamically typed language, true behaves differently depending on whether an equality (==) or identity (===) operator is used. Under loose comparison (==), PHP performs type juggling, coercing operands to booleans. Specific “falsy” values—such as 0, 0.0, "0", "", null, and empty arrays []—evaluate to false, while most other values evaluate to true. Under strict comparison (===), no type coercion occurs; the operand must be of type bool and hold the exact value of true. 
// Loose comparison (Type juggling occurs)
var_dump(true == 1);       // bool(true)
var_dump(true == "1");     // bool(true)
var_dump(true == "hello"); // bool(true)
var_dump(true == "0");     // bool(false)

// Strict comparison (Type and value must match)
var_dump(true === 1);       // bool(false)
var_dump(true === true);    // bool(true)

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Type Verification

To programmatically verify if a variable holds the exact boolean true state, strict comparison (===) is required. Relying solely on type-checking functions like is_bool() is insufficient, as it only verifies the data type and will return true even if the variable holds false. 
$value = true;

var_dump(is_bool($value));         // bool(true) - Only confirms type (could be false)
var_dump($value === true);         // bool(true) - Confirms both type and state
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