Exact rules governing consonant changes as seen in the first person singular in verb conjugations

Question

Apparently, in verbs ending in -ить (but maybe others are also concerned), the last letter of the stem for the first person singular changes according to the following pattern:

• д becomes ж as in ходить (to go by foot) for хожу
• з becomes ж as in возразить (to object, to disagree) for возражу
• c becomes ш as in спросить (to ask) for спрошу
• ст becomes щ as in простить (to forgive) for прощу
• т becomes ч as in ответить (to answer) for отвечу

But what are the complete set of rules and what is their entire field of application: only –ить verbs and only for first person singular or do we find other usages of these consonant permutations?

I have also seen for example that хотеть (to want) have also a permutation of consonant but not limited to the first person singular (хочу́): we also have хо́чешь and хо́чет. What are the rules in such a case then?

I have also found in a grammar textbook the following examples of apparent consonant mutations in adjectives/names:

• д: ж (медведь ‘bear’: медвежонок ‘bear-cub’);
• ст: щ (толстый ‘thick’: толщина ‘thickness’);
• ск: щ (трескаться ‘to crack’: трещина ‘crack’);
• т: ч (студент ‘student’: студенчество ‘student body’);
• ц: ч (заяц ‘hare’: зайчонок ‘leveret’; пловец ‘swimmer’: пловчиха ‘female swimmer’; перец ‘pepper’: перечница ‘pepper-pot’);
• г: ж (снег ‘snow’: снежинка ‘snow-flake’; шпага ‘sword’: шпажист ‘fencer’; прыгать ‘to jump’: прыжок ‘jump’; берег ‘shore’: побережье ‘coastline’);
• к: ч (великий ‘great’: величие ‘greatness’; but танк ‘tank’: танкист ‘tank-driver’?; мельник ‘miller’: мельничиха ‘miller’s wife’; волк ‘wolf’: волчица ‘she-wolf’; молоко ‘milk’: молочник ‘milk-jug’; спичка ‘match’: спичечница ‘matchbox stand’);
• х: ш (монах ‘monk’: монашество ‘monks’; горох ‘peas’: горошина ‘pea’ ; конюх ‘groom’: конюшня ‘stable’).

But this only adds to my confusion. What are the rules behind all these changes and are the rules covering all words or only specific subsets and if so, how?

Answer 1

I have found the following rules explaining consonant mutation in verbs with stem ending in a consonant.

Only some stem-end-consonants mutate and only into four other possible consonants:

• д, з, г mutate into ж
• т, ц, к mutate into ч
• с, х mutate into ш
• ст, ск mutate into щ

In first conjugation verbs (verbs using the -e- conjugation i.e. ending in -ю/-у, -ешь, -ет, -ем, -ете, -ют), the mutation happens in all forms of the present/future and imperative. E.g. пис-ать (to write, mutation between с and ш):

• Я пишу́
• Ты пи́шешь
• Он/Она/Оно пи́шет
• Мы пи́шем
• Вы пи́шете
• Они пи́шут

In second conjugation verbs (verbs using the -и-/-я- conjugation, i.e. ending in -ю, -ишь, -ит, -им, -ите, -ят), the mutation only takes place in the first person singular. E.g. трат-ить (to spend, mutation between т and ч) :

• Я тра́чу
• Ты тра́тишь
• Он, Она, Оно тра́тит
• Мы тра́тим
• Вы тра́тите
• Они тра́тят

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Could someone confirm that the above is a complete and exhaustive list of rules governing consonant mutations in verbs? Is it that simple or are there additional cases/exceptions to consider?

I have, for example, seen that verbs ending in -ти such as грести, идти, везти, нести... would not follow the above rules. Are there other exceptions?