Detailed Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Q: Why is the verb when paying for a service subscribe, but the noun form is subscription? Is there a rule that changes 'b' to 'p'?.
A:
The 'rule' goes right back to Latin (and probably to pre-Latin) where suffixes starting with an unvoiced consonant, such as '-tu' (earlier '-to') and '-si' caused a final voiced consonant on the root to be devoiced. Examples: scrib-o 'I write' -> scrip-si 'I have written', scrip-tum 'written' dirig-o 'I steer' -> direxi (direk-si) 'I have steered', direc-tum 'steered' So you see there are other similar pairs in English (eg 'dirigible' and 'direct' - though 'dirigible' is not a very common word, it's true) Unfortunately, rules like this that go all the way back to Latin, are not very useful to learners of English, because they don't always apply to every case that might appear similar. So although most English words that end in '-ibe' are derived from 'scribo', and have nouns in '-iption' (subscription, inscription, description, ascription), 'imbibe' is an exception: There is no noun '*imbiption'. And conversely, there are nouns in '-ruption' (disruption, corruption, interruption) but their corresponding verbs end in '-rupt', not '-rube' as you might have guessed.