Here, we will study a sort of verb that is related to the participles we've seen so far.
Consider the example below:
एतान् न हन्तुम् इच्छामि
etān na hantum icchāmi
I do not want to kill them.
It's difficult to see this from the example, but the word hantum is an uninflected participle, just like the gerund. But whereas the gerund specifies something that occurs before the main sentence, this new form occurs within it in an indefinite way. For that reason, this form is called the infinitive, meaning "the unlimited" or "the unbounded."
The infinitive is easy to form:
To form the infinitive, attach the suffix -tum to the verb root. Use the rules of the -tṛ suffix.
However, it's a little trickier to use. The infinitive is like an object to the main verb. But, the infinitive itself can have objects, too. For instance, consider the first example in this lesson. etān, which is the case 2 plural of etad, is the object of hantum. The two combine to create a more complex object: etān hantum, "to kill them." This phrase then becomes the object of the main verb icchāmi.
But the infinitive is not stuck in the "object" state. In fact, the infinitive can be paired with adjectives — as in "ready to kill" — or even nouns — as in "time to kill." In these senses, the infinitive is like a noun in case 4.
तस्मान्नार्हा वयं हन्तुं धार्तराष्ट्रान् स्वबन्धवान्
tasmānnārhā vayaṃ hantuṃ dhārtarāṣṭrān svabandhavān
Thus we are not entitled to kill the sons of Dhritarashtra, our own kinsmen. Bhagavad Gita 1.37
The infinitive can even be part of some compounds. It only appears in the bahuvrīhi compound, and it usually appears as the first member, after dropping the final -m. The second member of the compound is usually kāma, meaning "desire," or manas, meaning "mind."
योद्धुम् + कामः → योद्धुकामः
yoddhum + kāmaḥ → yoddhukāmaḥ
to fight + desire → with a desire to fight, wishing to fight
गन्तुम् + मनः → गन्तुमनः
gantum + manaḥ → gantumanaḥ
to go + mind → with a mind to go, thinking of going