κατανοητέον
From LSJ
λέγεις, ἃ δὲ λέγεις ἕνεκα τοῦ λαβεῖν λέγεις → you speak, but you say what you say for the sake of gain (Menander, fr. 776)
English (LSJ)
A one must observe, learn, Pl.Plt.305c, Porph.Marc.27; one must consider, πάλιν περί τινος Ph.1.83.
Greek (Liddell-Scott)
κατανοητέον: ῥημ. ἐπίθ., πρέπει νὰ μάθῃ τις, νὰ παρατηρήσῃ, Πλάτ. Πολιτ. 305C.