Alexander Schmidt, Shakespeare Lexicon and Quotation Dictionary

For, conj. 1) Used, as at present, to introduce a reason by a coordinate sentence (Fr. car, Germ. denn): “let's assist them, f. our case is as theirs,” Tp. I, 1, 58. “sit down, f. thou must now know farther,” I, 2, 33. 40 I, 2, 33 II, 1, 2. II, 1, 2 II, 1, 2 189 etc. etc.
2) Introducing a reason by a subordinate clause, == because, as: “and f., poor bird, thou singest not in the day, some dark deep desert will we find out,” Lucr. 1142. “but f. their virtue only is their show, they live unwooed,” Sonn. 54, 9. “and f. they looked but with divining eyes, they had not skill enough your worth to sing,” 106, 11. “and f. thou wast a spirit too delicate, . . . she did confine thee,” Tp. I, 2, 272. “my foolish rival that her father likes only f. his possessions are so huge,” Gentl. II, 4, 175. “I curse myself, f. they are sent by me, that they should harbour where their lord would be,” III, 1, 148. “you may not so extenuate his offence, f. I have had such faults,” Meas. II, 1, 28. “those, f. their parents were exceeding poor, I bought,” Err. I, 1, 57. “and f. the morning now is something worn, our purposed hunting shall be set aside,” Mids. IV, 1, 187. “why should this a desert be? f. it is unpeopled?” As III, 2, 134. “you are come in happy time, the rather f. I have some sport in hand,” Shr. Ind. 1, 91. Shr. I, 1, 92. All's III, 5, 45. All's III, 5, 45 Wint. III, 3, 33. IV, 4, 86. John II, 591. R2 I, 3, 127. R2 I, 3, 127 I, 4, 12. I, 4, 12 II, 1, 159. H6B I, 3, 169. R3 I, 1, 58. II, 2, 95. Cor. III, 1, 10. Tit. V, 1, 74. Lr. I, 1, 227. Oth. I, 3, 269 (Ff “when).” III, 3, 263. III, 3, 263 III, 4, 161. Cymb. III, 4, 54. IV, 2, 129.
For that, in the same sense: “f. that I love your daughter, I must advance the colours of my love,” Wiv. III, 4, 82. “which was broke off, partly f. that her promised proportions came short of composition,” Meas. V, 219. “else imputation, f. that he knew you, might reproach your life,” Meas. V, 219 “f. that it is not night when I do see your face, therefore I think I am not in the night,” Mids. II, 1, 220. Merch. I, 3, 44. Tw. III, 1, 166. Wint. IV, 4, 759. John V, 4, 42. R2 I, 1, 129. I, 3, 125. II, 1, 125. H6A II, 3, 31. II, 5, 71. V, 5, 80. H6C IV, 6, 11. Cor. I, 1, 117. I, 9, 47. III, 3, 93. Tit. III, 1, 40. Tim. II, 2, 209. Mcb. IV, 3, 185. Lr. I, 2, 5. Oth. I, 3, 24. II, 3, 234. Ant. III, 7, 30. Per. II, 1, 81.
For because, in the same sense: “why so? not f. because your brows are blacker,” Wint. II, 1, 7. “why rail I on this Commodity? but f. because he hath not wooed me yet,” John II, 588. “and f. because the world is populous, . . . . I cannot do it,” R2 V, 5, 3.
3) == in order that (followed by shall or should): “and f. the time shall not seem tedious, I'll tell thee what befel me,” H6C III, 1, 9. “love forswore me in my mother's womb, and f. I should not deal in her soft laws, she did corrupt frail nature,” III, 2, 154.
4) For to, followed by an inf., a) == in order to: “think women still to strive with men, to sin and never f. to saint,” Pilgr. 342. “send down Justice f. to wreak our wrongs,” Tit. IV, 3, 51. “which f. to prevent, I have thus set it down,” Hml. III, 1, 175 (Ff to, and “how to prevent). had not overboard thrown me f. to seek my mother,” Per. IV, 2, 71. b) to: “let your highness lay a more noble thought upon mine honour than f. to think . . . .,” All's V, 3, 181. “forbid the sea f. to obey the moon,” Wint. I, 2, 427. “here lacks but your mother f. to say amen,” Tit. IV, 2, 44. “we'll teach you f. to drink,” Hml. I, 2, 175 (Ff to drink deep). Shr. III, 2, 249.
5) Used as an expletive without meaning: “a pickaxe and a spade, a spade, f. and a shrouding sheet,” Hml. V, 1, 103 (song of the clown).
Concerning for why, see Why.