Abu al-Qasim, may Allah have mercy on him, said:

(Chapter: That by which purification [from water] is achieved)

The implied meaning is: This is a chapter on that by which purification [from water] is achieved. He omitted the subject (mubtada') because it is understood. His statement "[by which is achieved]" means it occurs and comes into being. It is used here in its complete (tamma) sense, not requiring a predicate (khabar). Whenever it is complete, it carries the meaning of occurrence and taking place. You say: "Kana al-amru" (The matter came to pass), meaning it happened and occurred. Allah the Almighty said: "And if he is in difficulty" (2:280), meaning: if one is found in difficulty. The poet said:

When winter comes, warm me up, for the old man is worn down by winter.

Meaning: when winter arrives and occurs.

In a manuscript read to Ibn 'Aqil, it is written: (Chapter: That with which purification is permissible, from water), and their meanings are similar.

Purification (tahara) linguistically means cleanliness from impurities. In the Sharia, it is the removal of that which prevents prayer, whether it be an act of ritual impurity (hadath) or filth (najasah), by means of water, or the removal of its legal status by means of soil. When the term "purification" is mentioned in the speech of the Lawgiver (the Prophet) or the discourse of the jurists, it refers to the technical Sharia definition [not the linguistic one; likewise, everything that has both a Sharia and a linguistic definition, the absolute use of the term refers to the Sharia definition] such as wudu' (ablution), prayer, fasting, zakat, hajj, and the like, because the apparent intent of the Lawgiver is to speak according to his specific technical definitions.

And "al-tuhur"—with a damma on the ta'—is the verbal noun (masdar), as stated by al-Yazidi.

"Al-tahur"—with a fatha—is among the transitive nouns, meaning that which purifies other things, like "al-ghasul" (that with which one washes).

Some of the Hanafis said: It is an intransitive noun, meaning it is synonymous with "tahir" (pure); for the Arabs do not differentiate between the "fa'il" form and the "fa'ul" form regarding transitivity and intransitivity. Thus, if the "fa'il" form is intransitive, its "fa'ul" form is also intransitive, evidenced by "qa'id" (sitting) and "qa'ud", "na'im" (sleeping) and "na'um", "darib" (striking) and "darub".

This is incorrect; for Allah the Almighty said: "...to purify you therewith" (8:11), and Jabir, may Allah be pleased with him, narrated that the Prophet -may Allah bless him and grant him peace- said: "I have been given five things which no Prophet before me was given: I have been granted victory through awe for a distance of a month's journey, and the earth has been made for me a place of worship and a means of purification (tahuran)." (Agreed upon). If he had meant only "tahir" (pure), there would have been no distinction, because it is pure for everyone. The Prophet -may Allah bless him and grant him peace- was asked about performing wudu' with seawater, and he said: "It is the purifier (al-tahur), its water is lawful, its dead are lawful." And if it were not...