-cial & -tial endings sound the same “shul”
special, confidential, initial, official

If you’re wondering why we have these two when one would do!
It’s all about the French and Latin origins of these words and the t or c in the original word:
potential – from late Latin potentialis, from potentia ‘power’, from potent- ‘being able’
facial – from medieval Latin facialis, from facies
initial – from Latin initialis, from initium ‘beginning’
(You don’t need to know French and Latin but it’s always good to know why spellings and words are the way they are.)

There’s a rule about which one to use but like all rules there are exceptions.

What’s the letter before these -cial words: social, special, beneficial?

What’s the letter before these -tial words: essential, substantial, partial?

Rule: Use -cial after a vowel, like after the vowel ‘o’ in social, ‘e’ in special, ‘i’ in beneficial

Use -tial after a consonant, especially, after ‘n’ in substantial, essential, ‘r’ in partial