Does the indefinite article 'a' in phrases 'motivating influence' and 'a chief inducement' need to be changed?

Appellant contends that the court erroneously instructed the jury by using the indefinite article 'a' in the phrases, 'a motivating influence,' and 'a chief inducement,' rather than the definite article 'the' in the same phrases. In Gillespie v. Rawlings, 49 Cal.2d 359, 364, 317 P.2d 601, the court observed that some cases have used 'the' in conjunction with the phrase 'motivating influence,' while others have used 'a.' The court reconciled these two lines of cases as follows: