・Japanese accent, based on the presence or absence of an akusento-kaku (アクセント核, accent nuclus, a steep drop in pitch), is first divided into two types (式): the accented with the akusento-kaku and the unaccented without the akusento-kaku. Yes, 'unaccented' is one type. Next, the accented words are classified as each pattern (型) according to the location of the akusento-kaku.  

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・When the akusento-kaku is on the first mora, it is called ichi-gata (1型, first-mora accent), on the second mora called ni-gata (2型, second-mora accent), on the third mora called san-gata  (3型, third-mora accent), etc. A word with no akusento-kaku, namely the unaccented, is called zero-gata (0型, no accent).  

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・A mora with the akusento-kaku is high-pitched, and the next mora is low-pitched.

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・As a general rule, the pitch of the first and second moras are different. Therefore, the possible accent pattern of a 3-mora word, for example, is one of HLL (ichi-gata, first-mora accent), LHL (ni-gata, second-mora accent), LHH (san-gata, third-mora accent) and LHH (zero-gata, no accent). If other accent patterns (LLH, HHL, HHH, etc.) appear, native speakers feel those are dialects, not standard Japanese.

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・When the akusento-kaku is on the last mora of a word (final mora accent, ni-gata of the 2-mora word, san-gata of the 3-mora word, yon-gata of the 4-mora word, etc.), you cannot tell the difference between final mora accent and no accent (zero-gata). By adding a particle such as が, we can tell the difference. The pitch of the particle of the final mora accent word is low, while that of no accent word remains high.

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Note: The second part of the long vowel (ー), small っ and ん cannot carry an akusento-kaku as well as i (い) of ai (あい、かい、がい、さい、ざい、たい、だい、ない、はい、ぱい、ばい、まい、らい). When the akusento-kaku falls on these moras, the askusento-kaku is shifted to the preceding mora.​

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