In Act One, Macbeth's plans & actions seem to be motivated most of all by whom/what?
a. Lust for riches and power
b.the support of the witches
c. Lady Macbeth's encouragement
d. the advice of Banquo
I have seen the options/priorities given by you. I would like to re-organize the same as hereunder:
a) the withes' proclamations on the heath;
b) Macbeth's own ambition;
c) Duncan's declaration that Malcolm would be the Prince of Cumberland;
d) Lady Macbeth's encouragement.
Let me now go into more details:
a) Witches' Proclamations-- the three witches meet Macbeth and Banquo on the heath; they hail Macbeth first as the thane of Glamis, then as the thane of Cawdor, and finally as the future king of Scotland. Macbeth, as Banquo observes, stands in a trance, 'rapt withal'. Soon Ross and Angus arrive and Macbeth comes to know how he has been rewarded with the title of the thane of Cawdor. Immediate fulfillment of the proclamation of the 2nd witch tempts Macbeth to believe that the 'greatest is behind'.
b) Macbeth's Own Ambition: Macbeth's reactions to the witches' proclamations and his being announced as the thane of Cawdor clearly indicate that there was a seed of evil ambition already in Macbeth. His asides in act 1 sc.3, reveal that he had 'horrible imaginings' as regards his ambition to achieve kingship.
c) Duncan's Declaration in Act 1 sc. 4: In this scene, Duncan declares that his eldest son, Malcolm, would be the Prince of Cumberland, and so the legitimate successor to the throne. This thwarts the chance of Macbeth's becoming the king, though in 11th century Scotland there was 'elective kingship'. As Duncan also declares his visit to Macbeth's castle that very night, Macbeth takes immediate leave of the king to ride to Inverness.
d) Lady Macbeth's Encouragement: Lady Macbeth receives her husband's letter and in her two soliloquies she resolves to chastise him with 'the valour of her tongue'. She apostrophizes to the powers of darkness to fortify her with the direst cruelty. It is she who plans the blueprint of the murder of Duncan, and gets the heinous 'deed' done by him.