par·ti·al·i·ty (n.) As title. why is the t slient in the word partiality?
But pronunciation does change. At one point there was just pronunciation and people devised spelling methods to capture what people say on paper faithfully. Spelling is very conservative - it doesn't like to change. But pronunciation changes faster.
One of the first hurdles in learning to read (because native speakers learn how to speak first before writing), are letters that don't seem to be pronounced, or are pronounced differently from the usual way.
In the example you gave, 'partiality', let's just look at the word 'partial'. The 't' is not pronounced as an explicit 't'. One could say that the 'ti' is pronounced as a 'sh' (which is itself problematic because it neither sounds like an 's' or an 'h').
The 't' in 'part' is pronounced as usual, so what happened when you add 'ial'?
In the suffix the 'i' is pronounced more like a 'y'. And a 'ty' often gets slurred into 'ch' (like in 'church') or even further like in 'potion'. In fact the 'ti' in 'partial' is acting just like the 'ti' in 'potion'.
So really it's not that the 't' in 'ti' is silent, but rather that things have moved on from the 'ty' sound all the way to an 'sh' sound.