This picture is about specific examples of these two suffixes.
Answer
Dictionary.com offers a good explanation
-al: a suffix with the general sense “of the kind of, pertaining to, having the form or character of” that named by the stem, occurring in loanwords from Latin ( autumnal; natural; pastoral ), and productive in English on the Latin model, usually with bases of Latin origin ( accidental; seasonal; tribal ). Originally, -al 1 was restricted to stems not containing an -l- (cf. -ar1); recent lapses in this rule have produced semantically distinct pairs, as familiar and familial.
https://www.dictionary.com/browse/-al
In brief: we usually use -al, but when a word ends with an “L” sound, we use -ar. I suppose that’s because some people (Latin people, perhaps) found it uncomfortable to pronounce words like “modulal”, “tablal” or “titlal.”
Note: dictionaries mark the -al suffix as “productive” (meaning that you can produce new words by joining the -al suffix to a noun), but like most things in English, its usage is not consistent.
Usage notes
If the root word contains l, the variant -ar is often used instead (e.g. solar, lunar, columnar, lumbar). Sometimes both forms are found: linear, lineal. One also sees -ial, as in manorial.As nominalizer, some verbs have two corresponding nouns, one ending in -al and the other in -tion/-sion (more common suffix), with one or the other being more common, sometimes with different nuances. Notable examples: disposition/disposal (dispose), proposition/proposal (propose), submission/submittal (submit), transmission/transmittal (transmit). Some superficial pairs are actually of different origin, notably reversion/reversal (revert/reverse, not both from reverse).
https://en.wiktionary.org/wiki/-al
Attribution
Source : Link , Question Author : Michael , Answer Author : Juhasz
