1) Able to be considered 2) Conceivable 3) Ponderable 4) Possible to ponder 5) Thinkable 1) Thinkable 
• (a.) Capable of being brought before the mind as a thought or idea; conceivable; thinkable.
Cog'i·ta·ble adjective [ Latin cogitabilis , from cogitare to think.] Capable of being brought before the mind as a thought or idea; conceivable; thinkable. « Creation is cogitable by us only as a putting forth of divine power. Sir W. Hamilton. » 
[adj] - possible to ponder
ponderable adjective capable of being thought about; `space flight to other galaxies becomes more cogitable`
able to be considered; conceivable; thinkable: The thought of space flights to other galaxies has become more cogitable.