SuttaCentral
Thanks, but it seems to mostly focus on later readings, it assumes the meaning and doesn’t really get into it. It seems a common thing, most authors I’ve seen more or less assume the basic meaning and start from there.
I did briefly look on academia for things and didn’t find this essay, so if you find anything else, please do share!
Wow, this text has considerably … changed 
since I first saw it!
So if I understand you correctly you are saying it means something along the lines:
“pertaining-to-the-source-wise” (yoniso) “in the mind” (manasi) “doing” (kāra)?
I.e. using the mind in a way that pertains to the source?
Still digesting … 
I am wondering if “applying the mind” is in fact more specific than “attending”? It seems to me still rather vague and general. But I find it hard to do any better …
Added:
Just wondering (while looking at MN 2): Do you in English “pay application of mind”?
When you pay irrational application of mind, defilements arise, and once arisen they grow. (MN 2:3.4)
Added again:
There’s also sammāmanasikāra (for example in DN 1:1.31.1), which would then be
“right” (sammā) “in the mind” (manasi) “doing” (kāra).
(Sanskrit) Grammatical POV for yoniśo manasikāraḥ/manaskāraḥ
Yoni means source, place of origin, womb etc.
yoniśas (or yoniśaḥ or yoniśo which are sandhi variants of the former) is yoni ending with the śas adverbial affix. It would normally have the meaning “according to each of their origins”, “by each place of origin”. By extension, it could also mean “completely” (i.e. “right from the origins onwards progressively until the end”)
Here the -śas suffix is a taddhita (nominal affix) and is used in the sense of enumerative ordering.
Other examples:
ekaikaśaḥ (eka-eka-śaḥ) or just eka-śaḥ = one by one, one after the other
dvi-śaḥ = two by two, two after two
yugma-śaḥ = pair by pair, pair after pair
varga-śaḥ = varga by varga, varga after varga
kati-śaḥ = how many after how many
bhāgaśaḥ (bhāgaso in pāli) = part by part, part after part
khaṇḍaśaḥ (pāli khaṇḍaso) = bit by bit, part after part
āyatanaśaḥ (pāli āyatanaso) = āyatanam by āyatanam (sphere by sphere)
dhātuśaḥ (pāli dhātuso) = dhātu by dhātu
etc.
Now for manaskāra/manasikāraḥ:
manas = mind.
manas-kāraḥ or manasi-kāraḥ (manasi = locative singular of manas) = placing in the mind, application of the mind, mental investigation
So yoniśaḥ manasikāraḥ I think means:
Investigating something mentally - thoroughly and progressively from its start to finish.
This topic is timely for me! In a JIBS article, a certain Aggadhamma states that " Yoniso mānasikāra is also a synonym of paccavekkhana which means wise consideration, contemplation, and reflection." He goes on to use suttas about yoniso mānasikāra to explain paccavekkhana. I’m not sure which Ven. Aggadhamma is this author or what their qualifications are. It seemed to me that paccavekkhana-suddhi is closer to appamāda, and yoniso mānasikāra closer to yathābhūtañāṇadassana
Yoni (womb), as mentioned above, seems to be referring to the direction origination, and from that point of view, yoniso manasikāra would be attention that takes origination into account. Or even more specifically, attention that takes truth into account. Attention that mirrors that of the four noble truths:
By not attending to things unfit for attention and by attending to things fit for attention, unarisen taints do not arise in him and arisen taints are abandoned.
“He attends wisely: ‘This is suffering’; he attends wisely: ‘This is the origin of suffering’; he attends wisely: ‘This is the cessation of suffering’; he attends wisely: ‘This is the way leading to the cessation of suffering.’ When he attends wisely in this way, three fetters are abandoned in him: personality view, doubt, and adherence to rules and observances. -MN 2
There are often a multitude of ways to consider why a certain experience manifests, and significance depends on the perspective: the direction of attention. For instance, there is often deep consideration for why there is either painful or [lack of] pleasant feeling in the experience, and an ordinary person who is unaware of the Dhamma will more often than not dwell on arrangement of circumstance to discover the reason for suffering (and attempt to mitigate it), failing to take into account that even if desirable circumstances are achieved, craving (in regard to feeling) - the true origin of suffering - remains unnoticed and untouched.
So, it isn’t enough to just investigate circumstance to discover why there is suffering - all that can tell is that there is suffering, in this way or that. And for the ordinary person, merely giving attention to circumstances in this way will most often give rise to sensuality, ill will, etc. To discern what is in the direction of yoni, as described in MN 2, the perspective must endure circumstances in order to discern the broader principles of suffering and craving. Same applies when investigating any form liability, which is how both impermanence and suffering apply to the experience: an enduring liability to change, and therefore cannot be me, not myself and not “I am”.
That subtle shift in attention changes the priority when it comes to freedom from suffering. Whereas the ordinary person would find a solution to suffering with a more agreeable arrangement of circumstance, the person training in Dhamma would go in the direction of developing the mind as to not be at the mercy of circumstance. So, any rendering should emphasize the placement of the mind/attention to the source/womb, which implies going through the particulars of a given experience to discern the principles that give it meaning. “Appropriate” or “wise” don’t necessarily fail to take this into account, but either does require some unpacking.
And it may well change again!
Yes, I think so. Perhaps it could be expressed even more loosely, “applying the mind in a manner that is guided by an awareness that the sources of things shape their manifestations.”
Happy to hear alternatives. But to me, “applying” is more active and ongoing. Attention is a little static, like soldiers standing at attention.
No, a mistake, I’ve fixed it.
“right application of mind” (which actually fits the context better.)
I’m sure there will be other cases, too!
This is one sense of the ending, and thanks for the examples. But in Pali at least—not sure about Sanskrit—this ending can take a number of senses. We previously discussed it a little here.
In this case, the commentary typically glosses it with an instrumental upāyena pathena.
Looking at couple of the other examples, it’s not clear to me that they all have an enumerative sense. Consider SN 22.57:
Idha, bhikkhave, bhikkhu dhātuso upaparikkhati, āyatanaso upaparikkhati, paṭiccasamuppādaso upaparikkhati.
Paṭiccasamuppāda is always treated in singular as an abstract principle, and one cannot examine “paṭiccasamuppāda by paṭiccasamuppāda”. Surely the instrumental applies here:
It’s when a mendicant examines by way of the elements, sense fields, and dependent origination.
As a different usage, consider āyatanaso in AN 4.61. There a householder is lauded for their financial prudence with the phrase:
Idamassa paṭhamaṁ ṭhānagataṁ hoti pattagataṁ āyatanaso paribhuttaṁ.
It’s not an easy idiom, (I have reconsidered and changed my translation just now), but I have rendered it as:
This is his first expenditure in an appropriate sphere on a deserved and fitting cause.
Here too the commentary glosses āyatanaso with an instrumental (kāraṇeneva).
Other cases are less clear. dhātuso could be “by way of the elements” or “element by element”.
Anyway, the main point is that the enumerative usage of the -so ending is just one application in Pali, but in relevant contexts the Pali tradition typically interprets the ablative in an instrumental sense.
I have been trying out the rendering “application of mind”. It seems to work fairly well.
Again, that article only considers the Buddhist usage, i.e. what it went to, not where it came from. That’s one half of the equation.
But sure, in general Buddhist usage that’s fine.
Umm, I’m not really sure what you’re getting at here. Appamada is “diligence”, which is not really the same as “reviewing”. Yoniso maniskara isn’t quite the same as yathābhūtañāṇadassana. Normally it leads to it, but sometimes the meaning overlaps, like when Yoniso maniskara is applied to the four noble truths.
I was just noting that yoniso manasi kāra is in no way a synonym for paccavekkhana, despite what the author Aggadhamma wrote. We see paccavekkhana in the exhortations to be diligent in reviewing or checking the skillful and unskillful deeds and states of mind, eg MN 61, AN 10.48, AN 10.51, AN 10.52, AN 10.53, AN 10.54, AN 8.7. While Yoniso manasi kāra is more about wisely choosing what to pay attention to, e.g to impermanence etc, and not to “what was I in the past” etc.
It would be very kind to notify us if this happens. 
Yes, exactly. My thoughts for German currently turn around a phrase that’s very similar to “apply”, in fact. … Not yet sure what comes out.
I also have to say, I am not too happy with “rational” for yoniso. Rational, to my ear anyway, sounds like a rather cold application of reason, with no emotional warmth. And I don’t understand the Buddhist way of using the mind to be of that sort.
Rather, a wise application of mind includes things like love and compassion, and the inspiration that comes from faith—these are not things that can be explained “rationally”. In fact, faith (a rather emotional thing) is said to be the very cause of yoniso manasi kāra, as per AN 10.61.
AN10.61:6.20: Ko cāhāro yonisomanasikārassa?
And what is the fuel for rational application of mind?
AN10.61:6.21: ‘Saddhā’tissa vacanīyaṁ.
You should say: ‘Faith.’
So currently I am still inclining more to the direction of “gründlich” (thorough, to the ground) rather than “rational” (would be the same word in German, or else “vernünftig”).
Perhaps “gründlicher (yoniso) Gebrauch des Geistes” versus “oberflächlicher (ayoniso) Gebrauch des Geistes”. Or maybe “ergründend” would be better—and a lot clumsier! I love your “loose” translation above! 
The four aspects of stream entry:
2. and 3. give rise to Right view, which is a feature of a stream entrant. 4. gives rise to yatabhutanana.
Therefore I prefer ‘wise contemplation’. It must be differentiated from sati, which is why 3. and 4. are distinct.
Hmm, in german we have a word “folgerichtig”, for instance “folgerichtiges Denken”. (Sherlock Holmes should be the master of such an ability of thinking… 
) I have always taken as hypothesis that something like this is meant, ability to think while aware of the source-effect-sequence. But I don’t know an english term which emits this nuance. DeepL proposes “consequent/logical/consistent/consequential thinking”, and LEO.org gives two more terms “congruously/coherent thinking”. One which sounds even more appropriate here is perhaps “deductive thinking” - this term focuses a technique in the thinking-process, while “consistent”,“congruously” and “coherent” rather focus the quality of the result of the thinking. “Logically thinking” is perhaps near, but seems more general than “deductive” which sounds to me more specific to point on the source-effect sequence in the process of thinking or of considering.
“Folgerichtig” is not bad. It comes close to “rational” in meaning, but sounds less cold.
The difference to “gründlich” or “ergründend” is perhaps that these move backwards from a given point to the source, while “folgerichtig” has more of a forward movement.
Nice to discuss German terms here! Thank you, @Nessie!
what about, in that direction, perhaps, “tiefgründig”?
Since the author is also considering the interpretation of the term in question by different teachers, here is the venerable Nyanamoli:
Sādhukam is also (often) combined with manasikāra. And this also has the sense of thoroughly. In ud1.1 for example ‘sādhukaṁ manasākāsi’ is used where you maybe would expect yoniso because it relates to depend origination. Do you think, Bhante, that sādhukam and yoniso are synonyms in this regard?
It seems in fact. What is described here for the Buddha is actually the same as what Buddha Vipassi does in DN 14 (where yoniso is used). Good example!
I think in Dutch it could work with one word as well maybe in German also? This would translate to something like this in German: ‘und ergründete das ,bedingte Entstehen’ in fortlaufender Richtung’ - ergründete is then a translation of sādhukam manasākāsi.
Hmm, I’m not in such a rush here. The vinaya parallel to this in Kd 1 just has anulomapaṭilomaṁ manasākāsi. Sanskrit parallel has vyavalokayan (“scrutinize”).
And elsewhere (eg. sn12.37:2.1) we find sādhukaṁ yoniso manasi karoti. And not forgetting that 150+ times sādhukaṁ manasi karoti is used to call the audience’s attention at the start of a talk.
I think they’re similar, but not full synonyms. Sādhukaṁ means “carefully, thoroughly”, whereas as I point out above, yoniso has a deep range of doctrinal and metaphorical connections. There’s a reason why it became one of the most characteristic Buddhist terms.
Thank you Bhante. I don’t have anything to offer, but I really like your use of the word trace here. It seems to encompass a lot of what is going on - investigation, finding, causal sequences.
I’m drifting in here a bit late… 
And I’d like to add the perspective of a gardener with a love of mathematics. Presenting this clearly and concisely is a bit of a struggle, so I beg patience in reading.
The present focus on “rationality” as a translation does not sit well with me. Rationality is simply a lever, and like any lever can be used skillfully or not. A lever can lift a load to benefit. It can also be a truncheon to oppress others into submission. Rationality is just a lever.
Rationality is also incomplete. The rigorous decomposition of arguments into axioms and logical derivations is incomplete. It also does not match the common experience of struggling with a vexing problem only to wake up in the clarity of morning to a solution derived through no rational experience.
And where does gardening fit in here? Well, as a rational person, I determinedly set about gardening with a rational mindset. And after years of effort I found the rational approach limited and incomplete, even to the point of actually being harmful. So I abandoned my electronics. I abandoned my software programs. I abandoned my fancy hydroponic chemicals. And I tried something different.
What I tried was gardening with an open heart.
And the garden breathed a sigh of relief. Insects returned. Birds showed up. The power failed and the plants laughed with joy. It has been quite remarkable. When I opened my heart to the garden, the earth responded in kind. When I fed the earth, it opened its arms and fed me in return.
So for me, the “yoniso manasi kaara” is just “well grounded with an open heart”. That’s a lot of words and I am not a wordsmith, but simply waving hands in a different direction.
“Rational” doesn’t mean “reductively analytical”, it means “with reason and understanding”.
To treat the natural world as a bunch of independent, definable and manipulable elements to be acted upon is irrational because that’s not how nature works. It is rational to respond to nature with empathy and intuition, because it is a system of interdependent networks of which we are a part.