The Mental Causation Question and Emergence

Dr. Umut Baysan–University Teacher in Philosophy at the University of Glasgow

How can the mind caus­ally influ­ence a world that is, ulti­mately, made up of phys­ic­al stuff? This is one way of ask­ing the men­tal caus­a­tion ques­tion, where men­tal caus­a­tion is the type of caus­a­tion in which either the cause or effect is a men­tal event or prop­erty. The ques­tion can also be put this way: How can men­tal events or prop­er­ties (such as beliefs, desires, sen­sa­tions, and so on) cause oth­er events? Discussion of the men­tal caus­a­tion ques­tion dates back to at least Princes Elizabeth of Bohemia’s chal­lenge to Descartes, who took the mind to be a non-physical sub­stance. Elizabeth’s ques­tion to Descartes was how one can make sense of the idea that the mind could move the body, or the body could influ­ence the mind, if they are two dis­tinct sub­stances as such.

We take men­tal caus­a­tion to be real. The real­ity of men­tal caus­a­tion is so cent­ral to our philo­soph­ic­al think­ing that the view that there is no such thing as men­tal caus­a­tion, namely epi­phen­om­en­al­ism, has a cru­cial dia­lect­ic­al role in philo­soph­ic­al argu­ment­a­tion in meta­phys­ics of mind. As with Elizabeth’s cri­ti­cism of Descartes, some­times views in the meta­phys­ics of mind are eval­u­ated on this basis. In terms of their roles in philo­soph­ic­al argu­ment­a­tion, I find epi­phen­om­en­al­ism and rad­ic­al scep­ti­cism to be very sim­il­ar. In epi­stem­o­logy, rad­ic­al scep­ti­cism is the view that there is no such thing as know­ledge of the extern­al world. Although pretty much every­one takes rad­ic­al scep­ti­cism to be false, some epi­stem­o­lo­gists still devote time to show­ing why this is the case, as a view’s implic­a­tion of rad­ic­al scep­ti­cism is taken to be reas­on enough to dis­pense with it. Likewise in meta­phys­ics of mind, nearly every­one thinks that epi­phen­om­en­al­ism is false, but there is a very siz­able lit­er­at­ure try­ing to show how this is so. For this reas­on, we often find charges of epi­phen­om­en­al­ism in reduc­tio argu­ments.

Although there may have been ways of tack­ling Princess Elizabeth’s chal­lenge to Descartes, the dif­fi­culty of doing so moved many con­tem­por­ary philo­soph­ers towards an onto­lo­gic­ally phys­ic­al­ist view accord­ing to which, at least in the actu­al world, there are only phys­ic­al sub­stances. Now, once we get rid of all non-physical sub­stances from our onto­logy (sub­stance phys­ic­al­ism) and yet still hold on to the exist­ence of minds (real­ism about the mind), the next set of ques­tions is: What should we do with the prop­er­ties of such minds? What are men­tal prop­er­ties? Can men­tal prop­er­ties be reduced to phys­ic­al properties?

For the sake of brev­ity, I shall not recite the reas­ons why such a reduc­tion can­not be main­tained, so let’s just assume that men­tal prop­er­ties are not phys­ic­al prop­er­ties. (For sem­in­al work on this point, see Putnam 1967.) In a world with purely phys­ic­al sub­stances, some of which have irre­du­cibly men­tal prop­er­ties, it might look as if the men­tal caus­a­tion ques­tion can be answered eas­ily. Mental events can cause phys­ic­al events (or vice versa); such a caus­al rela­tion doesn’t require the inter­ac­tion of phys­ic­al and non-physical sub­stances, so the prob­lem of caus­al inter­ac­tion evaporates.

Emergentism is a view, or rather a group of views, accord­ing to which sub­stance phys­ic­al­ism is true and men­tal prop­er­ties are irre­du­cibly men­tal. There are (at least) two vari­et­ies of emer­gen­t­ism. The weak vari­ety, which some­times goes by the name “non-reductive phys­ic­al­ism”, takes men­tal prop­er­ties to be real­ized by phys­ic­al prop­er­ties. (For my work on what it is for a prop­erty to be real­ized by anoth­er prop­erty, see Baysan 2015). The strong vari­ety, which goes by the name (sur­prise sur­prise!) “strong emer­gen­t­ism”, holds that (at least some) men­tal prop­er­ties are as fun­da­ment­al as phys­ic­al prop­er­ties to the extent that they need not be real­ised by phys­ic­al prop­er­ties. (See Barnes 2012 for an account of strong emer­gence along these lines. For joint dis­cus­sions of weak and strong emer­gence, see Chalmers 2006 and Wilson 2015.)

Some con­tem­por­ary meta­phys­i­cians of mind, most not­ably Jaegwon Kim (2005), think that epi­phen­om­en­al­ism is still a threat to emer­gen­t­ism. It is thought be a prob­lem for the weak, non-reductive phys­ic­al­ist, vari­ety because of the fol­low­ing line of thought. The phys­ic­al world is sup­posed to be caus­ally closed in the sense that if a phys­ic­al event has a cause at any time, then at that time, it has a suf­fi­cient phys­ic­al cause. Thus, if a phys­ic­al event is caused by a men­tal event (or a prop­erty), it must be fully caused by a phys­ic­al event (or a prop­erty) too. If all this is true, then every phys­ic­al event that has a men­tal cause must be caus­ally over­de­termined. (Here, the idea is that caus­a­tion implies determ­in­a­tion, and hav­ing more than one fully suf­fi­cient cause implies overdeterm­in­a­tion.) The accept­ance of such sys­tem­at­ic caus­al over­de­termin­a­tion is taken to be absurd; the world can’t have that much redund­ant caus­a­tion. Therefore, the com­bin­a­tion of non-reductive phys­ic­al­ism and the real­ity men­tal caus­a­tion is not ten­able. That is the charge anyway.

Now, what about strong emer­gen­t­ism? In a nut­shell, defend­ers of this view can reject the idea that the phys­ic­al domain is caus­ally closed in the way that non-reductive phys­ic­al­ists typ­ic­ally assume. Given its anti-physicalist assump­tion that some prop­er­ties oth­er than the phys­ic­al ones can be fun­da­ment­al too, reject­ing the caus­al clos­ure prin­ciple is def­in­itely a live option for strong emer­gen­t­ism. However, accord­ing to some, that is pre­cisely the prob­lem with this view. From a sci­entif­ic or nat­ur­al­ist­ic point of view, how can we defend such a view if its best way of accom­mod­at­ing men­tal caus­a­tion is through reject­ing the caus­al clos­ure of the phys­ic­al domain?

The pic­ture that I have por­trayed thus far seems to sug­gest that unless we go all the way and reduce men­tal prop­er­ties to phys­ic­al prop­er­ties, there isn’t any room for men­tal caus­a­tion. This is what Kim and oth­ers have been try­ing to per­suade us over the years. But, is the reas­on­ing that has led us here really sol­id? Should all of the argu­ment­at­ive steps briefly sketched above be accep­ted? I have some doubts.

First, there is an emer­ging (pun inten­ded) con­sensus that the caus­al argu­ment against non-reductive phys­ic­al­ism sketched above has some flaws. Some philo­soph­ers aren’t con­vinced that non-reductive phys­ic­al­ism, as Kim por­trays it, really implies caus­al over­de­termin­a­tion (see Yablo 1992 for a sem­in­al account). Very roughly, the idea is that such caus­al over­de­termin­a­tion appears to obtain when a whole event and its parts are caus­ing an event too. But tak­ing a whole and its parts sep­ar­ately is surely “double count­ing”. Also, in present­a­tions of the caus­al argu­ment against non-reductive phys­ic­al­ism, we often come across the idea that if an event has two dis­tinct suf­fi­cient causes, it must be genu­inely caus­ally overdetermined—this is known as “the exclu­sion prin­ciple”. But a prin­ciple with such a cru­cial dia­lect­ic­al role needs some backing-up, and some authors have noted that there doesn’t seem to be any pos­it­ive argu­ment for the truth of the exclu­sion prin­ciple. (For a cri­ti­cism along these lines, see Arnadottir and Crane 2013).

Second, the reas­on to res­ist strong emer­gen­t­ism that is sketched above can be ques­tioned too. Do we really have good reas­ons to think that the phys­ic­al domain is caus­ally closed? I don’t think that we can play the caus­al clos­ure card unless we care­fully study the reas­ons that are giv­en in favour of it. Considering its import­ance in argu­ment­a­tion in the meta­phys­ics of mind, it would be fair to say that there hasn’t been enough atten­tion giv­en to the pos­it­ive reas­ons for hold­ing it. I am aware of three argu­ments for the caus­al clos­ure prin­ciple: (1) Lycan’s (1987) argu­ment that it is absurd to think that laws of con­ser­va­tion hold every­where in the uni­verse with the excep­tion of the human skull; (2) McLaughlin’s (1992) sug­ges­tion that the fail­ure of the caus­al clos­ure prin­ciple was a sci­entif­ic hypo­thes­is in chem­istry which was even­tu­ally fals­i­fied (in chem­istry!); and (3) Papineau’s (2002) argu­ment that the prin­ciple is induct­ively veri­fied by the prac­tice of 20th cen­tury physiolo­gists. This is not the place to care­fully exam­ine these three argu­ments in detail, but I think it is fair to say that these argu­ments don’t even attempt to be con­clus­ive. The clos­ure prin­ciple may turn out to be true, but wheth­er that is the case or not will be an empir­ic­al mat­ter of fact, and until we some­how estab­lished it empir­ic­ally, we need to devise more sol­id philo­soph­ic­al argu­ments for it.

I hope this short dis­cus­sion has per­suaded you that whichever view in the meta­phys­ics of mind turns out to be true, the men­tal caus­a­tion ques­tion will play some role in determ­in­ing its plausibility.


Árnadóttir, S. and Crane, T. (2013). ‘There is no Exclusion Problem’, in Mental Causation and Ontology, eds. S. C. Gibb, E. J. Lowe, and R. D. Ingthorsson (Oxford: Oxford University Press).

Barnes, E. (2012). ‘Emergence and Fundamentality’. Mind, 121, pp. 873–901.

Baysan, U. (2015) ‘Realization Relations in Metaphysics’, Minds and Machines 25, pp. 247–60.

Chalmers, D. (2006). ‘Strong and Weak Emergence’, in The Re-Emergence of Emergence , eds. P. Clayton & P. Davies (Oxford: Oxford University Press).

Kim, J. (2005) Physicalism or Something Near Enough. Princeton, NJ: Princeton University Press.

Lycan, W. (1987). Consciousness. Cambridge, MA: MIT Press.

McLaughlin, B. (1992). ‘The Rise and Fall of British Emergentism’, in Emergence or Reduction?: Prospects for Nonreductive Physicalism, eds. A. Beckermann, H. & J. Kim (De Gruyter).

Papineau, D. (2002). Thinking about Consciousness. Oxford: Oxford University Press.

Putnam, H. (1967). ‘Psychological Predicates’, in Art, Mind, and Religion, eds. W.H. Capitan & D.D. Merrill (Pittsburgh: University of Pittsburgh Press).

Wilson, J. (2015). ‘Metaphysical Emergence: Weak and Strong’, in Metaphysics in Contemporary Physics: Poznan Studies in the Philosophy of the Sciences and the Humanities, eds. T. Bigaj and C. Wuthrich (Leiden: Brill).

Yablo, S. (1992) ‘Mental Causation’. Philosophical Review, 101, pp. 245–280.