Honkatori is a technique used to create waka (a traditional Japanese poem of thirty-one syllables) in the study of Japanese poems to take in one or two phrases of old and famous poem (the original) to create a new poem. This technique was used to give depth by using the original as a background and to make the expressive effect multilayered.
For example, see the poems below:
"Kokin Wakashu" (A Collection of Ancient and Modern Japanese Poetry) Volume 2, KI no Tsurayuki
Miwayama no Shika mo kakusu ka Harugasumi Hito ni shirarenu Hanaya sakuran' (Mt. Miwa is hidden so deeply by spring haze; Flowers that no one knows must be blossoming.)
"Manyoshu" (Collection of Ten Thousand Leaves) Volume 1, Nukata no Okimi
Miwayama no Shika mo kakusu ka Kumo danimo Kokoro aranamo Kakusoubeshi ya' (Mt. Miwa is hidden so deeply by clouds; Please be merciful, clouds, do not hide.)
As it is clear if you compare these two poems, Tsurayuki adopted the first and second phrases of Nukata no Okimi's poem and created the third and the rest by himself.
There are various reactions to such honkatori.
FUJIWARA no Kiyosuke of Rokujo Toke (the Rokujo Fujiwara family) made critical assessment as 'stealing old poems.'
On the other hand, FUJIWARA no Toshinari of the Mikohidari family evaluated it as an expression technique.
FUJIWARA no Teika, a child of Toshinari, summarized the principle of honkatori as follows in "Kindai shuka" (Superior poems of our time) and "Eiga taigai" (Essentials of Poetic Composition):
You can take less than two phrases when using them in the same positions as those in the original poem.
You can take up to two phrases and three to four letters when using them in different positions as those in the original poem.
Except famous poets' poems that are evaluated as excellent, it is allowed to use the first two phrases including Makura word (Poetic epithet convention) or jokotoba (a preface word) of the original.
The main theme should be different from that of the original.
The original should be taken from Sandaishu (three major collections of Japanese poetry; Collection of Ancient and Modern Japanese Poetry, Later Collection of Japanese Poetry and Collection of Japanese poetry compiled by imperial command), "Ise Monogatari" (The Tales of Ise), or "Sanjurokunin kashu" (Thirty-Six Anthologies), not from recent poetry (from the view point of Teika).