Substantial question of law requires more than party impact; it must be arguable, unsettled, or open to reasonable doubt.

A question of law under Article 133 is substantial only if it is important, difficult, fairly arguable, or open to reasonable doubt or difference of opinion; it is not substantial merely because it affects the parties' rights. A settled point or one already covered by authoritative precedent will not qualify. On res judicata, the earlier decree did not finally decide the validity of the assignment or otherwise conclusively bar the issue now raised, so the plea failed. On these principles, no leave could be justified on the basis of a substantial question of law, and the res judicata contention was rejected.

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Issues: (i) Whether the words "substantial question of law" in Article 133 of the Constitution of India mean every question of law affecting the rights of parties or only a question of law that is important, difficult, or open to reasonable doubt or difference of opinion; (ii) Whether the prior decree raised a bar of res judicata.

Issue (i): Whether the words "substantial question of law" in Article 133 of the Constitution of India mean every question of law affecting the rights of parties or only a question of law that is important, difficult, or open to reasonable doubt or difference of opinion.

Analysis: The Full Bench held that the word "substantial" qualifies the expression "question of law" and not merely the effect of the question on the parties' rights. A question of law is substantial when it is fairly arguable, when there is room for reasonable doubt or difference of opinion, when the point is not settled by the highest authority, or when the legal principle requires consideration of alternative views. A mere application of settled principles, or a question already covered by authoritative precedent, is not enough.

Conclusion: Any question of law affecting the rights of parties is not substantial by itself. It is substantial only if it is important, difficult, or open to reasonable doubt or difference of opinion.

Issue (ii): Whether the prior decree raised a bar of res judicata.

Analysis: The prior proceeding had left the validity of the assignment open, and the relevant issue was not finally decided against the applicant. On the facts stated, the earlier decree did not conclusively determine the matter now sought to be raised, so the bar of res judicata was not established.

Conclusion: The plea of res judicata failed.

Final Conclusion: The application could not succeed because no substantial question of law warranting leave was made out, and the res judicata contention also failed.

Ratio Decidendi: A substantial question of law under Article 133 exists only when the legal issue is substantial in the sense of being important, difficult, fairly arguable, or open to reasonable doubt or difference of opinion; a question does not become substantial merely because it affects the parties' rights.

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