Gottfried Keller was a German composer who emigrated to England around 1680. Three years after his death, his only music theory book was published in 1707 as A Compleat Method for attaining to Play a Thorough Bass. On pages 8 and 9 he gives four examples of using the suspension of a 4th at a cadence, focusing on the chord before and after the suspension itself.
As was typical in the Baroque period, a suspension was a dissonant note that had to be prepared in the previous chord as a consonant note and resolved in the chord that follows the dissonance as another consonant note.
So in all four examples, the C in the top part is consonant on the second crotchet (quarter-note) beat, then held over in the same part to become a dissonant 4th on the third crotchet beat, before resolving by a downwards step into a (consonant) 3rd on the last beat of the bar. As this 3rd to the bass is the leading note, it then needs to go back up to the tonic note in the final chord.
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