Causal clauses & verbal nouns
The conjugation because to build a causal sentence can in its simplest way also be created by concatenating two main clauses and by using the word ஏனென்றால்｢ēṉeṉṟāl｣ in between.
Another — more common — way to form a causal sentence is by making use of verbal nouns together with the "instrumental" case of nouns.
The verbal noun is similar to making adjectives a noun. If you add -அது｢-atu｣ to the verb stem + tense suffix, you get the nominalized verb.
செய்｢cey｣ + கின்று｢kiṉṟu｣ + அது｢atu｣ = செய்கின்றது｢ceykiṉṟatu｣
செய்｢cey｣ + த்｢t｣ + அது｢atu｣ = செய்தது｢ceytatu｣
செய்｢cey｣ + வ்｢v｣ + அது｢atu｣ = செய்வது｢ceyvatu｣
The negative form is created by adding ஆத்｢āt｣ + அது｢atu｣ to the verb stem:
செய்｢cey｣ + ஆத்｢āt｣ + அது｢atu｣ = செய்யாதது｢ceyyātatu｣
It's hard to translate these phrases directly into English as there is no similar grammatical rule but you can compare it to something like "to jump" becoming "the jumping".
However, in Tamil, "the jumping" can be in three different tenses: "the jumping", "the jumped", "the to jump". And it can even existing in the negated form: "the not jumping".
Now with this knowledge, if you want to build a causal sentence, you use this verbal noun (which is now not a verb but a noun) in the third case by using ஆல்｢āl｣ for the sub-clause.
வரு｢varu｣ = verb to come
வரு｢varu｣ + கின்று｢kiṉṟu｣ + அது｢atu｣ = வருகின்றது｢varukiṉṟatu｣ ⇒ verbal noun the coming
வருகின்றது｢varukiṉṟatu｣ + ஆல்｢āl｣ = வருகின்றதால்｢varukiṉṟatāl｣ ⇒ verbal noun in instrumental because of the coming.
If you create a causal sentence using the concept, the subclause with the reason will always be the first part: