Hebrew gates are two-letter sub-roots. Since position of letters in a word contributes to the meaning of word, when two-letters are reversed, they have a related meaning which we can compare because of the shared letters. But they also have some sort of reversal in the meaning which makes the two forms contrast.

As an example: Father 'ab' אב is the reverse gate of 'come' 'ba' בא. In English it does not appear to be related. We must go the formation of the words, enter in to the metaphoric idea, and then pop back out into the words.

Father אב is 'After God spoke and created the heavens and the earth א... After he separated his creation from himself א... After there was a war between heaven and earth א... God revealed himself to man ב.

Come בא is 'God reveled himself to man ב and then The firmament joined the face of the waters א... there was morning to join Night to Day א, and evening to join Day to Night א... There was reconciliation between heaven and earth א.' And the Father said, 'Come' ^{[1] [2] [3]}

This page (http://sensusplenior.net/wiki/Category:Gates) is a collector page. Articles on gates will have a tag which will automatically index then here.