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What is the difference between “ɪ”, "i", “i:”? Is “ɪ” lax and short, "i" tense and short, "i:" tense and long?

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You can hear what the IPA letters are supposed to sound like here. The terminological difference is that [i] is "close" and [ɪ] is "near-close", but non-IPA tradition tems that distinction "tense" and "lax", though sometimes it is treated as respectively [+ATR] and [–ATR]. The ordinary letter ":" is not official IPA, but it is widely used instead of official "ː" to indicate segmental length. But when applied to English, "i" is highly ambiguous, so you'd have to determine the interpretation from context.

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Basically, [ɪ] (near-close front unrounded vowel) is like the < i > in fish, [i] (close front unrounded vowel) is like the < ee > in feet, and [iː] is the same as the latter, but longer.

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    The vowel in feet is /iː/ in transcription systems that use all three. Short, tense /i/ is normally reserved for the final vowel in tiny, adverbs in -ly, etc. – Janus Bahs Jacquet Apr 26 '20 at 15:01
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    Well pointed @JanusBahsJacquet! – Ergative Man Apr 26 '20 at 15:57