もしないで

The grammar pattern もしないで expresses "without even doing" something, emphasizing that the subject neglected or failed to perform even a basic or expected action before doing something else. It conveys a sense of criticism, surprise, or frustration that the action was not performed at all.

The pattern is formed by taking the ます-stem of a verb and attaching もしないで. The し in もしないで comes from する, so the literal structure is "without even doing [verb]."

Nuance of criticism or disbelief

This pattern strongly implies that the speaker finds it unreasonable or unacceptable that the action was skipped. It often carries a reproachful or exasperated tone.

Compare with the simpler ～ないで ("without doing"), which is neutral. もしないで adds the nuance of "not even", making the omission feel more egregious:

• たべないで食べないででかけた出かけた – "went out without eating" (neutral)
• たべ食べもしないででかけた出かけた – "went out without even eating" (critical/emphatic)

Related pattern: もせずに

A more formal or literary equivalent is もせずに, which carries the same meaning but uses せず (the classical negative of する) instead of しないで.