Ideas are the most fundamental instruments of thought.  Under­stand­ing how ideas signify will clarify a number of confusions. 

    Signs are means of knowing.  Signifiers are only potential signs unless they actually evoke a thought.  Smoke, though a potential sign of fire, is operative only when used to know fire.  Since knowing is relational, so are signs.  John of St.  Thomas (John Poinsot, 1589-1644) makes an im­por­tant dis­tinc­tion between formal and instrumental signs.[i]  An instrumental sign requires that we under­stand own nature before it can signify.  A formal sign does not. 

    Smoke and road markers are instrumental signs.  For smoke to signify fire one must know the dark smear on the horizon is smoke and not dust.  For a road sign to inform one the road turns right ahead, it must be recognized as marker and the form of its arrow grasped.  This is a ternary relationship there is a signifier, an idea elicited in a subject, and what is signified.[ii] Imagine seeing Tut­an­­­khamen’s mummy at a time before hieroglyphics were decoded.  It bears a cartouche saying “Tutan­khamen.”  Here we the have signifier and signified, but the signifier is inoperative until interpreted.  For actual signification, we need all three relata.[iii]

    Ideas are not instrumental signs.   I need not grasp that <apple> is an idea, or even think of ideas, to grasp the signified apple.  <Apple> signifies apples directly and trans­­parently.  Only on reflec­tion do I realize that apples are known by means of <apple> ideas.  <Apple> is a formal sign. “ A formal sign is one whose whole nature and being are simply a repre­senting, or a meaning, or a signify­ing of some­thing else,”[iv] as opposed to instru­mental signs whose natures were combustion products, paint on metal, or ink on mum­­my wrappings.

    A similar distinction has been independently noted by Frank Jackson, of Mary’s Room fame.  He writes:

there is a marked contrast between, on the one hand, the way representational devices like maps and sentences represent, and, on the other, the way perceptual experience represents.  There is a gap between vehicle of representation and what is represented in the first case that does not exist in the second.[v]

There is no necessary connection between sentences or the isobars on a weather maps and what they represent.  Thoughts, however, invariably represent what they intend.  The gap between maps and sentences, and what they represent is filled by an interpreter as a third element.

    Formal signification is a binary, not a ternary relation.  The signifier is not separate from the per­­son understanding it.  My idea <apple> is just me thinking of an apple.  The word “apple” can only signify by evoking the idea <apple>.  To signify it uses all the elements to think <apple> plus the word itself.  Instrumental signs require one more relatum than formal signs.

    Ideas are in a different class than observed brain and computer states.  To understand what a computer state signifies we need to grasp a represen­tation of it such as dis­played characters.  When it is grasped, we may see the computer state as representing something just as paint on a road marker can represent a curving road­.  So computer states signify as instrumental signs.  If an observer knew what your brain state signified, it would be as an in­stru­mental sign for her.  For you, the situation is very different.  You do not use your brain state as a sign because we don’t know our brain states, but their content.  We don’t know which synapses are active, or our neural firing rates – the data encoding contents.

    Third-person observations of the brain use instrumental signif­ica­tion and a ternary relationship. First-person awareness involves formal sig­nif­ica­tion and a binary relationship. In the third-person view of a brain or computer, subjectivity is confined to the observer.  In the first-person case, we grasp information directly, with­out knowing our brain state.  The analogy be­tween human thought and computer processing confuses these two types of signification.

    The ternary computer signification depends on binary formal significa­tion.  Computers actually signify only when they evoke an idea in people, who then intend what is signified.  Computer states have no actual significance without an interpreting subject, while human ideas always involve an aware subject.  Therefore, computers do not “think.”

    Ric Machuga (2002) brings out another important semiotic distinction: the difference in dynamics between causal and intentional signification.  When an animal smells smoke, it will respond with fire avoiding behavior.  We can describe this as a case of using smoke as a sign of fire, but to do so is to use “sign” in an equivocal way.  When we humans use signs, our responses are generally mediated by concepts and judgements.  When animals use signs, there is no need to appeal to such mediation.  Physical mechanisms provide a completely adequate explanation of the data.  Morgan's canon, a psychological application of Ockham’s razor, tells us:

In no case is an animal activity to be interpreted in terms of higher psychological processes, if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development.[vi]

Thus, we are quite justified in saying that we need posit no intentional mechanisms in such uses of signs by animals.  Evolution and neurophysiology cover all the bases.

    On the other hand, human signing is not so explained. To see this clearly, consider our use of language. Evolution does not explain why the concept <water> is signified by acqua, eau, wasser, etc.  depending on where you live.  These signs have no physically necessary relation to what they signify, but are products of human thought.  Similarly, when we offer an argument to effect a change of mind or action, the argument does not work in a purely physical way.  If it did, then we would not expect different embodiments (written vs.  oral, Greek vs.  English) of the same thought to be equally effective for their communities.