In Malay, nearly all roots are bisyllabic. There are a few exceptions; but monosyllabic roots tend to add an extra syllable when there is a prefix, empasising the bisyllabic expectation for roots. For example:
- cap ('stamp') becomes mengecap ('to stamp'), not *mencap
- cat ('paint') becomes pengecat ('painter'), not *pencat
- sah ('valid') becomes mengesahkan ('to confirm'), not *menyahkan
Note that baik ('good') and laut ('sea') are bisyllabic, so there is no need for this extra syllable:
- baik ('good') becomes membaiki ('to improve'), not *mengebaiki
- laut ('sea') becomes pelaut ('sailor'), not *pengelaut
However, I have no explanation why tahu ('to know') becomes mengetahui ('to know') rather than the expected *menahui. Why is the extra syllable added? Perhaps there is a feeling that tahu is monosyllabic, as the /h/ is weak (or sometimes omitted).