The adjective- and noun-forming -al suffix can be added both to base words (personal) and words that already contain suffixes, primarily the -ic and -tion suffix (medical and national). This suffix is stress-controlling, meaning it dictates where the primary stress can be expected to fall within a word.
2-syllable -al words
Words that contain the -al
suffix that are only two syllables in length are usually stressed on the first syllable (as are most 2-syllable nouns and adjectives, regardless of the presence of a suffix).
3+ syllable -al words
Words that are three syllables or longer that contain the -al suffix are usually stressed on the third-from-last syllable.
-ic and -tion + -al
The -al suffix can be added to the -ic suffix and -tion suffix and the word will still be stressed on the third-from-last syllable. This is consistent with the fact that words containing the -ic or -tion are usually stressed on the syllable previous to the -ic or -tion.