@Josh ********
Obviously the letters with the "silent mark" over them are silent. But the issue is that there are some words that just have a silent letter with no rule associated with. Similar to any other language. My textbook has rules for 5 different letters that should be silent, but there are also 2 other rules that say as follows:
1) Sometimes consonants can just be silent without a silent mark at all
ปรารถนา has a silent ร
สามารถ has a silent ร
ไทย has a silent ย
พุทธ has a silent ธ
2) You can see some other cases apart from the previous rules about -ติ and -ตุ where the vowel is not pronounced
ภูมิใจ has a silent . ิ
พยาธิ has a silent . ิ