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One way to show passage of time is by referring to time-based events. Over the course of a year you can use seasons for this; if we see your characters walking through the snow, and next see them ...
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Source: https://writers.stackexchange.com/a/21172 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
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One way to show passage of time is by referring to time-based events. Over the course of a year you can use seasons for this; if we see your characters walking through the snow, and next see them walking through the fall leaves, we know that at least half a year has passed. For multi-year spans, look for milestone events: a graduating student who we last saw entering college, somebody celebrating his five-year anniversary at the job, the birth and progress of children (could be relatives/friends and not your characters), the first fruit from the tree they planted as a sapling in the earlier part, whatever works in your story. Another way, if you're using the close-character POV, is to use your characters' thoughts: "Had it really been three years already since (prominent event from the earlier part)?" and the like.