The fourteen difficult questions of the "heretics" to which the Buddha made no reply, for, as it is said, the questions were no more properly put than if one asked " How much milk can you get from cow's horn?" They are forms of: All is permanent, impermanent, both or neither; all changes, changes not, both, neither; at death a spirit departs, does not, both, neither; after death we have the same body (or personality) and spirit, or body and spirit are different.

A Dictionary of Chinese Buddhist Terms, William Edward Soothill and Lewis Hodous

（名數）外道十四難句，佛不答之。一、世界及我為常耶？二、世界及我為無常耶？三、世界及我為亦有常亦無常耶？四、世界及我為非有常非無常耶？五、世界及我為有邊耶？六、世界及我為無邊耶？七、世界及我為亦有邊亦無邊耶？八、世界及我為非有邊非無邊耶？九、死後有神去耶？十、死後無神去耶？十一、死後亦有神去亦無神去耶？十二、死後亦非有神去亦非無神去耶？十三、後世是身是神耶？十四、身異神異耶？問曰：若佛為一切智人何不答此十四難？答曰：無此事實，故不答。諸法有常無此理，諸法斷亦無此理，以是故佛不答。譬如人問搆牛角得幾汁之乳？是為非問。不可答也。出智度論二，俱舍論十九。

丁福保《佛學大辭典》