the principle of the thing; the way things work; the natural order of things
Refers to the fundamental logic, reason, or natural law behind how things are or should be. Often used when explaining why something is inevitable or justifiable.
Act with an understanding of the way things work.
His explanation accords with the principle of the thing.
理屈 often refers to theoretical reasoning or argument, sometimes with a negative nuance of sophistry. 物の道理 is more about fundamental, self-evident truth.
Standard kanji spelling.
Mixed kana-kanji spelling, sometimes used for clarity or emphasis.
Compound of 物 (もの, 'thing') + の (possessive particle) + 道理 (どうり, 'reason, principle'). Literally 'the principle of things'.