After reading Majjhima Nikaya 26, this question always pops into my mind: How can one attain the formless dimensions without going first through 4th jhana? What type of meditation makes this possible?
https://suttacentral.net/en/mn26
“Thus Āḷāra Kālāma, my teacher, placed me, his pupil, on an equal footing with himself and awarded me the highest honour. But it occurred to me: ‘This Dhamma does not lead to disenchantment, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna, but only to reappearance in the base of nothingness. Not being satisfied with that Dhamma, disappointed with it, I left.’
“Thus Uddaka Rāmaputta, my companion in the holy life, placed me in the position of a teacher and accorded me the highest honour. But it occurred to me: ‘This Dhamma does not lead to disenchantment, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna, but only to reappearance in the base of neither-perception-nor-non-perception.’ Not being satisfied with that Dhamma, disappointed with it, I left.