Because versus since: name the cause.
A cause differs from a starting point in time. English permits “since” to express either relationship. I recommend “because” when a writer wants to state a reason explicitly.
By Adam Frick · First draftThe match was cancelled because of heavy rain.
The pitch has been closed since Monday.
A reader should be able to distinguish a cause from a sequence of events. English gives “since” more than one job, including the introduction of a reason and a starting point in time. Context often resolves the meaning without difficulty. For shared professional English, I recommend giving “because” the causal job and reserving “since” for time wherever that division fits the sentence.
Examine a real explanation.
This is one of the reasons why an electrical substitution radiometer was chosen, since it is inherently stable.
An electrical substitution radiometer was chosen partly because the instrument is inherently stable.
The published sentence clearly concerns a reason for choosing an instrument. My revision makes that reason explicit with “because”, names the instrument instead of using a pronoun and removes the opening backward reference. The word “partly” preserves the source’s qualification that stability was one reason among others. The revision loses the original’s explicit link to the previous sentence, which discusses the need for stability. A full edit should check whether that link needs to be restored.
NASA’s use of “since” is grammatical. Cambridge’s account of “since” recognises both temporal and causal uses. My preference narrows the choice for a practical purpose. I want the connective itself to identify the relationship as far as possible, without asking context to do all the work.
Separate time from explanation.
Since the laboratory changed its method, the results have varied.
The results have varied since the laboratory changed its method.
The results have varied because the laboratory changed its method.
The first sentence allows a reader to consider a temporal connection or a causal explanation. The second foregrounds the period following the change, although readers may still infer a cause. The third expressly attributes the variation to the changed method. That attribution needs evidence, because an event occurring first does not establish that the event caused the next observation.
A careful writer must choose the relationship before choosing the connective. Replacing every “since” with “because” could strengthen a claim beyond the evidence. A time reference may be exactly what the research supports. Grammar should express the strength of the explanation rather than quietly increase that strength.
Give the connective a specific job.
Find each use of “since” in a draft. Decide whether the sentence names a reason or locates an event in time. For a reason, try “because” and check whether the evidence supports the resulting claim. For a time reference, retain “since” or name the period more explicitly.
My proposed division is a writing discipline, not a description of every accepted English usage. A native speaker may understand the original perfectly well. An international reader deserves an equally explicit route through the argument. I would rather make the relationship visible than rely entirely on familiarity with a flexible little word.