Can we know that хоро́ший and высо́кий declines differently based on their ending consonant?

Question

I read the Russian Declension Wikipedia article, which gives several examples for different adjective declensions.

The article explains that masculine adjectives ending in the nominative in ий and neuters in ее are declined as follows:
его (read: ево), ему, им, and ем.

This explains the difference between the declensions of хоро́ший and высо́кий, as the former Neuter is хоро́шее, while the latter is высо́кое.

My question is pretty of a yes/no nature:
Can we know that these two declines differently just based on their masculine form + the ending consonant?
In other words, can the different declensions of хоро́ший and высо́кий be explained in terms of the different function of the letters ш and к?

Answer 1

You actually got it right, here's the set of rules:

• If the root ends with к, г, x - in neuter it ends with -ое
• If the root ends with ж, ш, ч, щ - if masculine ends with -ий, if by -ой, then in neuter it ends with -ее
• If the root ends with palatalized н, then in neuter the ending would be -ее
• Otherwise for -ый we got -ое, for -oй it's -о́е

Answer 2

Yes, the adjectives with the stem ending in a soft consonant have -его in genitive, those with the stem ending in a hard one have -ого.

Adjectives in -кий, -гий, -хий have -ого in genitive because these three consonants are weak in modern Russian, meaning that the following vowel defines their palatalization, not the other way around as for the rest of the consonants.

Historically, they are all hard, and in some Russian dialects, most notably the Old Moscow dialect, they are even pronounced hard before the adjectives' endings (русскый, not русский).

Those adjectives also end in -ое in neuter: мягкий/мягкое, упругий/упругое, лопоухий/лопоухое

Answer 3

Yes, but not quite.

Here are all the possible sets of endings for masculine adjectives:

╔════╦══════════╦══════════╦════════╦══════════╦══════════╦═════════╦══════════╦════════╗
║    ║ Hard     ║ Hard     ║ Soft   ║ Sibilant ║ Sibilant ║ Glottal ║ Glottal  ║ Ц      ║
║    ║          ║ Stressed ║        ║          ║ Stressed ║         ║ Stressed ║        ║
╠════╬══════════╬══════════╬════════╬══════════╬══════════╬═════════╬══════════╬════════╣
║ N. ║ кра́сный  ║ родно́й   ║ си́ний  ║ све́жий   ║ большо́й  ║ я́ркий   ║ сухо́й    ║ ку́цый  ║
╠════╬══════════╬══════════╬════════╬══════════╬══════════╬═════════╬══════════╬════════╣
║ G. ║ кра́сного ║ родно́го  ║ си́него ║ све́жего  ║ большо́го ║ я́ркого  ║ сухо́го   ║ ку́цего ║
╠════╬══════════╬══════════╬════════╬══════════╬══════════╬═════════╬══════════╬════════╣
║ D. ║ кра́сному ║ родно́му  ║ си́нему ║ све́жему  ║ большо́му ║ я́ркому  ║ сухо́му   ║ ку́цему ║
╠════╬══════════╬══════════╬════════╬══════════╬══════════╬═════════╬══════════╬════════╣
║ I. ║ кра́сным  ║ родны́м   ║ си́ним  ║ све́жим   ║ больши́м  ║ я́рким   ║ сухи́м    ║ ку́цым  ║
╠════╬══════════╬══════════╬════════╬══════════╬══════════╬═════════╬══════════╬════════╣
║ P. ║ кра́сном  ║ родно́м   ║ си́нем  ║ све́жем   ║ большо́м  ║ я́рком   ║ сухо́м    ║ ку́цем  ║
╚════╩══════════╩══════════╩════════╩══════════╩══════════╩═════════╩══════════╩════════╝

As you correctly noted, the declension depends on the last consonant of the stem which can be either:

• Hard (кра́сный, родно́й)
• Soft (си́ний, ка́рий)
• Glottal: г, к, х
• Sibilant: ж, ш, щ, ч
• or ц.

And when it comes to endings starting with -о (-ого, -ом), the position of the stress: the -о will change into -е in unstressed positions after soft and sibilant consonants as well as ц.

If you want to be all the way analytical about this, just memorise the endings in the Hard column (-ого, -ому, -ым, -ем), and then apply these replacements to the first vowel of the ending depending on the stem type and the stress:

╔═══════════╦═══════════╗
║ Hard or Ц ║ Otherwise ║
║ Either    ║ Either    ║
╠═══════════╬═══════════╣
║ -а        ║ -я        ║
╠═══════════╬═══════════╣
║ -у        ║ -ю        ║
╠═══════════╬═══════════╣
║ -ы        ║ -и        ║
╚═══════════╩═══════════╝
╔════════╦══════╦══════════╦══════════╦═════════════╦═════════╦════════╦══════════╗
║ Hard   ║ Soft ║ Soft     ║ Sibilant ║ Sibilant    ║ Glottal ║ Ц      ║ Ц        ║
║ Either ║ Uns. ║ Stressed ║ Unstr.   ║ Stressed    ║ Either  ║ Unstr. ║ Stressed ║
╠════════╬══════╬══════════╬══════════╬═════════════╬═════════╬════════╬══════════╣
║ -о     ║ -е   ║ -ё       ║ -е       ║ -о          ║ -о      ║ -е     ║ -о       ║
║        ║      ║          ║          ║ -ё in verbs ║         ║        ║          ║
╚════════╩══════╩══════════╩══════════╩═════════════╩═════════╩════════╩══════════╝

(This only works in oblique cases but usually we already know the nominative, right?)

To go from masculine to neuter/feminine/plural, change the ending to -ое/-ая/-ые and apply the above replacements to the first vowel of the ending.

The good news is these replacements are quite universal across the language and work for other parts of speech and as well as other parts of the word (suffixes):

• ма́мой - ня́ней - ка́шей - лапшо́й - му́хой - землёй (feminine instrumental endings)

• танцева́ть - пританцо́вывать, тушева́ть - затушёвывать (verbal suffix)

• лило́вый - вишнёвый - бе́жевый - со́евый (adjectival suffix)

• мо́ем - че́шем - печём - поём (3rd person plural verbal endings)

I know this could be a bit too much to take in one bite. In case you get lost there's software tools to help you out:

• хромой косой синий полувыспавшийся куцый заяц