A direct object is a word that receives action. Another way to think about a direct object is to find the verb of the sentence, and then ask the question "Whom or what received the action of the verb?"
In the sentence "I drink water", the word "drink" indicates the action of the sentence. The action is drinking. To find the direct object, ask the question "What is being drunk?" The answer is "water". Therefore, "water" is the direct object of the sentence.
It is important to remember that the suffix for direct objects is a case suffix. Therefore, words that end in -டு, -று, and -ம் add case suffixes according to different rules than do all other nouns.Ex:
(In the second example, the word "cut" is the verb, which means it is the action. To find the direct object, ask "Whom/What is being cut?" Here, it is the tree, which means it is the direct object.)
Already, we have seen one difference between case suffixes and other ("non-case") suffixes, which is that words undergo changes before adding case suffixes. As we will see in later lessons, there is another difference between these 2 categories of suffixes:
In the first example, the direct object is a compound, since two things are being seen. We need to add the case suffix -ஐ for both words since they are direct objects, and we also need to add the non-case suffix -உம் to both words since they are a part of a compound phrase. According to the rule, -ஐ is added first, and then -உம் is added.