っこない

1. 1There is no way someone can do something; states flatly that an action is impossible, typically with a potential verb.Ex. 1
2. 2There is no way something will happen or someone would do something; expresses strong certainty that it won't occur.Ex. 2

A casual, emotional expression used in everyday speech among friends and family. It is often used to dismiss a possibility or to reassure someone, as with 信じてよ in example 2. It is subjective and emphatic, and much blunter than the more neutral はずがない or わけがない.

• わけがないN3「わけがない」also strongly denies possibility, focusing on reasoning and common sense; it can attach to verbs, adjectives, and nouns, and works in both spoken and written language. When attaching to verbs, the two are often interchangeable, but「っこない」is more casual and more emotional.
• はずがないN4「はずがない」also means "impossible," usually inferred from logic or common sense, with a neutral register, and it can also attach to adjectives and nouns. With verbs they are often interchangeable, but「っこない」is more casual and emphatic, and cannot express one's own volition.
• まいN2「まい」can also express negative volition ("will never..."), which「っこない」cannot; only in the negative-conjecture sense are they similar, but「まい」is milder and more literary, usually attaching to the dictionary form of verbs, and can also attach to nouns and adjectives (e.g.,「ではあるまい」).
• ものかN2「ものか」, besides denying possibility, can express the speaker's refusal of "I'll never..." (e.g.,「行くものか」), a usage「っこない」lacks;「ものか」can also attach to adjectives and「noun＋な」. When denying possibility with verbs attached, the two are broadly interchangeable.
• そうもないN3「そうもない」also attaches to the ます-stem of verbs and often pairs with potential verbs, but it conjectures from the situation or signs at hand that "it doesn't look like... will happen," with a mild tone and neutral register.「っこない」is a subjective, emphatic denial and very colloquial; swapping the two changes the tone considerably.
• やしないN1「やしない」also attaches to the ます-stem and is colloquial; when meaning "simply cannot do," it is interchangeable with「っこない」. However, when denying someone else's actions it often carries displeasure or contempt; it also has the past form「やしなかった」and the more literary「はしない」.

わけがない and はずがない also deny possibility, but they are more neutral and grounded in logic or expectation, while っこない is a casual, emotional dismissal. まい is a written or formal negative conjecture, ものか is an emotional retort or refusal, そうもない frames the judgment as a forecast of poor prospects, which can be strong (できそうもない "I don't see any way I can do it"), rather than a flat denial, and やしない is a colloquial emphatic negation of the action itself rather than of its possibility.