Now, by ordinary common sense knowledge, if I say: "There is no next birth," that is not authoritative. Because authoritative knowledge is . . . suppose from Bhagavad-gītā, next life is accepted. Tathā dehāntara-prāptir dhīras tatra na muhyati (BG 2.13). The beginning of Bhagavad-gītā is to teach that soul is eternal, it is migrating from one body to another, so there is next life. That is authoritative knowledge. But if somebody says that, "There is no birth," that is not authoritative. That is a layman's statement.
So a layman can put up his own theory in so many ways. Then what shall be the conclusion? The conclusion should be to take authoritative knowledge from authorities—one who is beyond the four defects of common man: one who does not make any mistake, one who is not illusioned, one who does not cheat, and one whose senses are perfect. We are devoid of all these qualification. We commit mistake, we are illusioned, we cheat, and at the same time, our senses are imperfect. So how we can give by speculation perfect knowledge? That is not possible.
Therefore our principle, Vedic principle, is to receive knowledge from the perfect. So-called scientists, so-called philosophers . . . because basically they're imperfect, how they can give you perfect? They can speak something, "Perhaps it is like that," "Maybe like that," "Perhaps it was like that." All their theories are like that. But actual fact is different. Actual fact we get from the Supreme Person, Kṛṣṇa, that dehāntara-prāptiḥ, tathā dehāntara-prāptir dhīras tatra na muhyati (BG 2.13). Dhīra: one who is sober.
There are two classes of men: dhīra and adhīra. Dhīra means sober, and adhīra means mad after sense gratification. That is called adhīra. So our Kṛṣṇa consciousness movement is so nice, dhīrādhīra. What is that? Kṛṣṇotkīrtana-gāna-nartana-parau premāmṛtāmbho-nidhī dhīrādhīra-priyau (Śrī Śrī Ṣaḍ Gosvāmy Aṣṭaka 1). Dhīrādhīra-priyau: it is pleasing both to the dhīra and the adhīra.