Aramaic did not have Brahmi's aspirated consonants (kh, th, etc.), whereas Brahmi did not have Aramaic's emphatic consonants (q, ṭ, ṣ), and it appears that these unneeded emphatic letters filled in for some of Brahmi's aspirates: Aramaic q for Brahmi kh, Aramaic ṭ (Θ) for Brahmi th (ʘ), etc. And just where Aramaic did not have a corresponding emphatic stop, p, Brahmi seems to have doubled up for the corresponding aspirate: Brahmi p and ph are graphically very similar, as if taken from the same source in Aramaic p. Bühler saw a systematic derivational principle for the other aspirates ch, jh, ph, bh, and dh, which involved adding a curve or upward hook to the right side of the character (which has been speculated to derive from h, ), while d and ṭ (not to be confused with the Semitic emphatic ṭ) were derived by back formation from dh and ṭh.[27]