もので

Gives a reason or circumstance, usually as a personal excuse or apologetic explanation for an undesirable result: 'because, since, the thing is…'. It is often used when apologizing for or justifying one's own actions.

Common in everyday speech, especially when explaining why something went wrong or when apologizing. It sounds slightly softer and more polite than ものだから. The main clause typically states a result that has already happened or could not be helped, and unlike ので or から, もので stresses that the speaker could not help the situation.

• ものだからN2「ものだから」 has essentially the same meaning and formation as 「もので」, and the two are interchangeable in most situations; however, it is more colloquial and carries a stronger tone of personal excuse, often used with 「〜てしまう」. In more formal situations, 「もので」 is the more appropriate choice.
• ものN2「もの」 is used at the end of a sentence to add a reason or support a previous judgment; it is colloquial and carries a whiny or dissatisfied tone, so use it cautiously with superiors. 「もので」 connects to a following clause mid-sentence and is more formal. Nouns and な-adjectives take 「だもの」, which differs from 「なもので」.
• こととてN1「こととて」 also gives a reason for asking forgiveness, but its tone is archaic and formal, appearing mostly in written contexts such as apology letters, and is unsuitable for everyday speech. Nouns take 「の」, as in 「子供のこととて」, and it is often paired with 「何分」.
• のでN5「ので」 focuses on objectively stating cause and effect without emphasizing an excusing nuance, and can also be used to explain being late and apologize; the following clause can state a result, judgment, request, or suggestion. Replacing 「もので」 with 「ので」 in a sentence generally works, but the excusing tone becomes weaker.
• からN5「から」 also has a usage indicating a starting point; when expressing a reason, its tone is subjective and direct, and the following clause can contain commands or invitations, with nouns and な-adjectives taking 「だ／ですから」. 「もので」 carries an excusing tone and cannot be followed by commands or invitations, making it more appropriate when apologizing.
• だってN2When 「だって」 expresses an excuse, it stands alone at the start of the sentence with the reason in the following clause, often ending with 「もん」, and has a whiny, defiant tone typical of casual speech; 「もので」 follows the reason clause and offers a polite apology, usable even with superiors. The two cannot be directly interchanged.

ものだから carries the same excuse-giving meaning but is more casual, sentence-final もの and だって are colloquial, sometimes plaintive justifications or objections, and こととて is an archaic, formal written equivalent. ので and から are neutral reason markers without the excuse nuance, and から freely allows commands and requests in the main clause.