The McGowan v. Parish case in 1912 revolved around a dispute over the validity of a will and testament. The decedent, Mr. Parish, had left his entire estate to Mrs. McGowan, who was not related to him by blood or marriage but had cared for him during his final years of illness. His siblings contested the will on grounds that he lacked mental capacity at the time it was made due to alcoholism and morphine addiction; they also alleged undue influence from Mrs.McGowan. The Supreme Court ruled in favor of Mrs.McGowan based on evidence presented which showed that despite Mr.Parish's addictions, he still possessed sufficient mental capacity when making his will as testified by witnesses including doctors who attended him during this period . Furthermore , there were no substantial proofs indicating any coercion or manipulation exerted by Mrs.McGowan upon Mr.Parish while drafting the said document. This ruling upheld an individual’s right to dispose their property through a validly executed last will and testament provided they possess sound mind at its execution regardless of physical infirmities or substance dependencies.

The dissenting opinion in the case of McGowan v. Parish argued that the court majority had erred in its interpretation and application of legal principles related to contract law, specifically those concerning mutual assent and consideration. The dissent contended that there was no valid contract between the parties because there was no meeting of minds or mutual agreement on essential terms, such as price or quantity. Furthermore, it asserted that even if a contract did exist, it lacked sufficient consideration since one party's promise to sell property at an unspecified future date did not constitute a legally enforceable obligation. Therefore, according to this view, any subsequent actions taken by either party based on this alleged agreement should be deemed void and unenforceable.