It is undoubtedly well settled that if the agreement to pay rent is dependent upon the performance by the landlord of some undertaking on his part, the failure by the landlord so to perform is a good defense to an action for the rent. It is equally well settled that if the agreements are independent such failure by the landlord is no defense. The difficulty arises in determining whether the agreements are dependent or independent. That question is one of construction, and it cannot be expected that all the cases may be satisfactorily reconciled. Two very late cases involving this question are of interest.
Aigler, Ralph W. "Breach of Landlord's Covenant as Defense to Action for Rent." Mich. L. Rev. 13 (1915): 317-8.