«ولكل جملة ركنان: محكوم عليه، ومحكوم به»
Every sentence has two basic elements: that about which a judgment is made and what is predicated of it.
Maḥkūm ʿalayh = musnad ilayh: the subject about which something is asserted.
Maḥkūm bihi = musnad: the property or event predicated of it.
“الْعِلْمُ نَافِعٌ”
“Knowledge is beneficial.”
Here “الْعِلْمُ” is musnad ilayh and “نَافِعٌ” is musnad. A relation of benefit is predicated of knowledge. Knowing these roles is necessary for later discussion of omission, mention, fronting and postponement.