Why (false and false or true) returns true

var_dump(false and false || true);
// result: bool(false)

(false and false || true) returns false as expected.

var_dump(false and false or true);
// result: bool(true)

but (false and false or true) returns true. I have no logical explanation why this is happening.

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&& and || have higher precedence on and and or

You can see Operator precedence on PHP documentation

So

<?php 
var_dump(false and false || true);
// eq: false and (true or false) => false

var_dump(false and false or true);
// eq: (false and false) or true => true

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Look at http://php.net/manual/en/language.operators.precedence.php

When we sort operators by priority, it´s:

&& > || > AND > OR

And it´s answer to your question. || has higher priority than AND .

I suppose you to use only one 'type' of logical operators, use && and || or and and or . Don´t combine them.

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Even though logically || and or are the same, their precendnce is not.

|| is of a higher precedence than OR , therefore they are interpreted differently in your 2 statements. I guess if you add a bracket around, it will have the same results:

(false and (false || true));

OR

(false and (false or true));

More here

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