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Everyone, from monolinguals to polyglots, has an accent (訛り) or distinct way of talking based on one's dialect or first language(s). "Accent" can also refer to the combination of various phonetic properties attributed to words that are imposed over the individual sounds making up its syllables, which translates to アクセント. 

Take for instance the word "debris." In American English, the "accented" syllable is on the second syllable, whereas in British English, the accented syllable is on the first syllable. From this one word, a lot can be gleaned about how accent systems work across language. One, accented parts of a word stand out. Two, accumulated differences regarding accent placement can result in regional accents, and native speakers are generally aware of how different dialects phonotactically contrast in this manner.

English has a "stress/dynamic" accent system (強弱アクセント) in which syllables differ in how much stress is put on syllables. "Stress" is the relative emphasis on certain syllables accompanied with increased loudness and vowel lengthening.

If, however, accented syllables only differ by pitch alone, the language is said to have a pitch accent (高低アクセント), which is what characterizes Standard Japanese as well as the overwhelming majority of its dialects. 

Terminology Note: 訛り and アクセント both translate to "accent," but they refer to two different understandings of the word "accent." In this introduction's first paragraph, "accent" is being used in the same sense as 訛り, which refers to the overall way a person's speech sounds, which is tied strongly to their background. On the other hand, アクセント directly relates to "pitch accent," which determines which morae are spoken with a higher pitch. 

Japanese pitch accent is given little attention in textbooks, but it is not out of sheer negligence that resources, including IMABI, do not typically provide accent notation for sentences much less individual words. Reasons for this omission include:

1. Of the 120 million or so native Japanese speakers, those who natively speak the normative pitch accent of Standard Japanese, based on the Yamanote Dialect of Tokyo proper, are confined to the greater Tokyo area, and although much of the country still uses the Tokyo-type pitch accent system (~60%), individual words may differ greatly in their assigned accent or lack thereof. Meaning, the system itself defines the patterns which phrases may take, but which pattern is lexically assigned to a given word may vary regionally. 

2. How native speakers perceive standard pitch accent is an oversimplification of what is linguistically true, and posited linguistic theories that seek to accurately describe it also vary in complexity. Typically, as is implied by the name of the system in Japanese - 高低アクセント - every mora is assigned a high (高) or low (低) pitch, but acoustically speaking, not all low and high pitches are equal in sound quality. To account for this discrepancy, some advocate viewing Japanese pitch accent as a tertiary system rather than a binary system (a discussion to be had in this lesson).

3. As is evident by the leading accent dictionaries published for native speakers such as the NHK日本語発音アクセント辞典, with every edition, numerous edits are made. This is not to say that earlier editions are inherently faulty, but intense research has been shaping how pitch accent ought to be perceived, at least for the sake of the general public.

4. Most importantly, even among Tokyoites, just as some words die out and new words are formed to represent the living world around us, the accent patterns of words themselves are also subject to change over time. A native Tokyoite in his 20s will not accent words the same as a native Tokyoite in his 20s will 100 years from now. The Tokyo Dialect (東京弁・東京方言), which is the basis of Standard Japanese, is at the southern end of the Eastern Japanese branch of the dialect continuum. The majority of said continuum exhibits an accent system known as 無アクセント in which all phrases are reduced to the 平板型 pattern. These terms are to be explained within our discussion, but to briefly put them into perspective, such a simplification of the current standard pitch accent is very much underway and will be become more and more prevalent as the 21st century progresses. 

5. Perhaps the crux as to why even Japanese script doesn't even distinguish pitch is that a non-native speaker can be understood even if an entire utterance's pitch contour(s) were 'wrong' provided the sentence were grammatically sound. The same cannot be said of a non-native speaker mispronouncing the tone of every word in a Mandarin sentence. In this light, Japanese is not viewed as a tonal language despite individual syllables (morae※) possessing a low or high tone. This statement holds true despite minimal pairs existing between words which only differ in pitch accent because those pairs only exist in the confines of Standard Japanese and do not take into account intelligible dialectal pronunciations. If pitch accent were so detrimental as tone, Japanese dialects would not be as intelligible among each other as they currently are, nor would foreign speakers be so easily understood. 

To combat all these factors in our formal discussion of pitch, a few ground rules will need to be laid out.

1. All lexically assigned pitch contours will be in accordance with the 2016 edition of  NHK日本語発音アクセント辞典, known specifically by the title NHK発音アクセント新辞典. 

2. Variant pitch contours will be listed by most to least preferred. Those in () are allowed in broadcasting but are still avoided in careful speech. 

3. Although the Japanese pitch accent system can be alternatively analyzed as a tertiary system to best reflect speech onset and post-accent acoustic tendencies, because accent dictionaries are formatted to reflect the widely accepted binary system hypothesis, L (low) tones and H (high) tones are meant to be understood as being relative pitch assignments to the surrounding morae. 

※Rather than utilizing syllables, Japanese utilizes what are known as "morae" (拍) which are individual units of speech equal in length and may be composed of a vowel or consonant + vowel (independent mora/自立拍) or a special mora (特殊拍) such as っ or ん. 

A frequently mentioned reason for why proper pitch is important to speech is that it helps distinguish otherwise homophonous phrases. This statement is true in the sense that there are countless minimal pairs made by differences in pitch accent.

For instance, both 生命 (life) and 声明 (proclamation) are pronounced as せいめい, but the former's pitch is HLLL and the latter's pitch is LHHL. As an extreme example, the following sentence is often presented:

1. 庭には2羽鶏がいる。
ニワニハ・ニワ・ニワトリガ・イル。
LHHL・HL・LHHHH・L※H
There are two chickens in the courtyard.

More so than individual words (語) themselves, pitch pattern assignment is best understood by segmenting sentences into 句 (phrases). 

Pitch Note: The ※ in Ex. 1 indicates environmentally based pitch flattening which renders the L mora in いる・居る as HH although no word is internalized as having such a pitch pattern in Standard Japanese. Such "pitch flattening" in between segments is naturally caused by mankind's inability to sound robotic. Even within relatively small phrases (whether they be isolated or juxtaposed with other phrases), changes in pitch over the course of a phrase are best understood to be gradual rather than abrupt. 

Though the 'standard' implementation of pitch accent is key to sounding like a native Tokyoite, there are two scenarios which disprove the necessity of its accurate implementation as a whole.

1. The Inability to Distinguish Non-Accent Words from Last-Mora-Accented Words

There are four different pitch accent contours that exist in Standard Japanese: 

1.  頭高型: Phrases whose accent is on the first mora.
2.  中高型: Phrase whose accent is on neither the first nor the last mora.
3.  尾高型: Word whose accent is on the last mora.
   
4.  平板型: An accent-less phrase whose pitch is maintained high even with affixes.

2. The Variability in Accent Across Dialects

As the last mention of other dialects' pitch accents, basic lexical items in Japanese differing in pitch across dialects certainly doesn't help build the case of pitch being quintessential to comprehension. 

※The historically correct accented mora in 花婿 is on the third mora (LHHL), but in the 日本語発音アクセント新辞典, the preferred placement of the accent is on the second mora (LHLL).  

Aside from the empty spaces which are impossible due to mora count, the four pitch contour patterns naturally manifest in phrases greater than six morae. For instance, 両刀使い is composed of seven morae and follows the 中高型 pattern with the accent on the fifth mora.