No matter who your narrator is, they're the person the reader sees the novel through. A tight first person, and omniscient third, everything is filtered through their eyes. Sometimes this filter is invisible and the reader doesn't feel any distance between them and the point of view (POV) character. Other times the filters are obvious and the reader feels the wall between them and the characters. One looks through the eyes of the POV, the other looks at the POV.
So, what exactly is filtering?
Words that distance the reader from the POV character.
Filter words remind the reader they're reading, explain things that are obvious, and often lead a writer into telling or crafting passive sentences. (Please note passive sentences are different from passive verbs)
(Here's more on passive voice)
Words like: saw, heard, felt, knew, watched, decided, noticed, realized, wondered, thought, looked.
Even worse, filter words are often found with their passive, telling cousins: to see, to hear, could tell, to watch, to decide, to notice, to realize, to wonder, to think, to look.
A POV character by definition is relaying everything they see, hear, feel, touch, smell, think. If it's described, we know they experienced it in some way. Using these words is redundant at best, clunky and telling at worst. Let's look at some examples:
Bob saw three zombies shambling toward him. (or worse) Bob could see three zombies shambling toward him.Look at these same sentences without those filter words:
Jane heard a scream from the hotel bathroom. (or worse) Jane could hear a scream from the hotel bathroom.
Sally knew she had to get out of there. (or worse) Sally could tell she had to get out of there.
I felt the cold metal of the shotgun against my back. (or worse) I could feel the cold metal of the shotgun against my back.
Three zombies shambled toward Bob.They're more active, more in the moment, and give a sense of immediacy. It also eliminates that told feeling.
A scream echoed from the hotel bathroom.
Sally had to get out of there. (or better) She had to get out of there.
Cold metal pressed against my back.
Some filter words are a little more ambiguous. The wondered, realized, decided, noticed, type.
Bob realized he'd have to make a run for it.In most cases, eliminating the filter words makes it stronger.
Jane wondered if they'd make it out of there alive.
Sally decided they'd just have to jump and see what happened.
I noticed the shotgun was missing.
He'd have to make a run for it.Sometimes you want that filter word if it's important to draw attention to that act (the feeling, hearing, watching), or it just sounds more dramatic with that filter. (This works well for chapter or scene enders) You might also want more filters if you're doing a far narrative distance or a omniscient narrator.
Would they'd make it out of there alive?
They'd just have to jump and see what happened.
Oh crap, where's the shotgun?
Bob watched the perimeter, eyes and ears alert for zombies.You don't have to cut every instance of these words, but they are good things to double check to make sure you're writing the strongest sentence you can. Filter words typically show up in told prose, passive prose, or just weak writing. You also find them in unintentionally distant POVs.
Jane closed her eyes and wondered if any of them would survive til dawn.
(Here are some more thoughts on POV and narrative distance)
Remember, your POV is already filtering for you. There's no need to remind the reader they're doing it.
Do you filter? Is it intentional or unintentional? If intentional, why?