A compound subject consists of two or more words acting as the subject of the sentence. When the series is joined conjunctively, that is, with the word and, in the vast majority of cases the subject is plural and requires a plural verb. Look at the following mistakes:
But recent research and commentary has [have] suggested that the emphasis upon eyewitness identification may lead to questionable results. Charles P. Curtis, Jr., Lions Under the Throne, p. 49 (1947) (quoted in Garner Legal, p. 841).
Note that research and commentary are two different things; the verb must be the plural have.
At the same time, the democratic process and the personal participation of the citizen in his government is [are] not all we want. Garner Legal, p. 841.
Note that democratic process and personal participation are two different things; hence the plural are.
Sometimes two nouns joined with and refer to a single idea and should carry a singular verb. Study this example:
The confusion and uncertainty is compounded by doubt regarding the question whether the complete liquidation and reorganization provisions can have concurrent application. Garner Legal, p. 841.
The words confusion and uncertainty actually describe a single mental state; the verb, therefore, is singular.