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This picture is about specific examples of these two suffixes.

closed as off-topic by Nathan Tuggy, Andrew, Eddie Kal, Varun Nair, James K Dec 9 '18 at 18:29

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  • What do you mean by "same"? Are you asking if they can be interchanged, so that one can say "Lightning is a naturar electricar phenomenon"? Or are you asking whether they mean the same thing, "of or pertaining to"? Or are you asking whether they are in fact different spellings of the same root, distinguished in order to make words more euphonious? – Nathan Tuggy Nov 28 '18 at 10:11
  • Yes, I want to ask whether they are interchangeable. If they are not, why ? Because of the meaning they denote,or? – JuJu Pig Nov 28 '18 at 12:48

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).

  • What does this sentence mean? “recent lapses in this rule have produced semantically distinct pairs, as familiar and familial.” – JuJu Pig Nov 29 '18 at 7:55
  • @JuJuPig, it means there was a rule that any noun with an "L" would use the suffix -ar, not -al; but sometimes (recently) this rule is broken and we use the -al suffix even on nouns ending in L's. One example is the word family; you would expect the adjective to use -ar, and it does: familiar. But we also have a word that breaks the L -> -ar rule: familial. These two words have distinct meanings. – Juhasz Nov 29 '18 at 14:25

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