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A recent question on this site ("to suspect" vs "to be suspicious of") asks about the difference between "to suspect" and "to be suspicious of." An even more complicated situation involves when to use suspect as an adjective (as in "suspect reasoning" or "a suspect classification") and when to use suspicious (as in "suspicious thoughts" or "a suspicious detective"). Is there a general rule about when to use one adjective or the other? Are they always interchangeable? A somewhat similar question comes up in an older query titled "that things were suspicious".

In this connection I note Wilson Follett's comment (under transitive/intransitive) in Modern American Usage (1966): "Thus, suspicious should designate the persons harboring a suspicion and suspect the person who is the object of it. From this it follows that one cannot be seen carrying a suitcase in a suspicious manner." Presumably, Follett wants the author to use "in a suspect manner" here.

Follett's analysis is clearly prescriptive and just as clearly ignores centuries of frequent contrary usage; but is there any validity to his prescription as a way for writers to avoid possible ambiguity, as in the case of "suspicious behavior" versus "suspect behavior"?

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Google NGRAM certainly sides with your centuries of use: – mplungjan Feb 11 '13 at 6:30
I agree with the comment in the other question that suspect is geared towards a specific "crime" and suspicious is more the air about the person – mplungjan Feb 11 '13 at 6:33

If Follett is trying to draw a distinction between suspect and suspicious when coupled to words like manner, behaviour then I think he's simply mistaken. But there are contexts where the choice of adjectival form makes a difference. For example...

1 The driver software for my printer is suspect (it may contain bugs, and thus not work properly).
2 The driver software for my printer is suspicious (it may contain malware, and infect my computer).

What those examples illustrate is that something is suspect if you have reason to believe (suspect) that it may be the cause of a problem (often, a problem you're already aware of). Note that the reason you singled out the driver software may have nothing to do with the thing in and of itself. Maybe your computer worked fine until you updated the driver, but now it crashes intermittently. It's suspect by inference, not by appearance.

You normally say something is suspicious because it looks or behaves in a manner that suggests malicious intent. That's why I say it doesn't make sense to distinguish between suspect/suspicious behaviour in most contexts - it will always be understood as suspicious whichever word you use.

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A suspect detective has perhaps committed a crime
A suspicious detective is the person suspecting that something is suspicious about someone else

I agree with the comment in the other question that suspect is geared towards a specific "crime" and suspicious is more the air about the person.

I agree with you on the Follett comment - I would personally expect a suspect to carry his suitcase in a suspicious manner (e.g. there is an air about the way he is carrying it)

If we look at the definitions on the web


* Having or showing a cautious distrust of someone or something.
* Causing one to have the idea or impression that something or someone is of questionable, dishonest, or dangerous character or condition.
distrustful - doubtful - fishy - suspect - mistrustful



Not to be relied on or trusted; possibly dangerous or false: "a suspect package was found".
verb. doubt - mistrust - misdoubt - distrust - question
adjective. suspicious - doubtful - fishy - questionable - dubious

I see the same "air about".

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But note that by the definition you quoted for 'suspicious', the suspicious detective may be one who looks funny, acts strangely, and makes you think he might be involved in shady dealings. (in other words, makes you suspicious of him rather than himself being suspicious of a third party.) – einpoklum Feb 11 '13 at 9:17
I still hear a huge difference between he was suspicious (of) and he looked suspicious – mplungjan Feb 11 '13 at 9:31

protected by RegDwigнt Feb 11 '13 at 16:53

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